Nobody Gets Left Behind: Keeping Your Squad Alive Through the Suicide Mission
One of the neat things about Mass Effect 2 is that first time you play it, you can't help but feel a little dread and uncertainty about the final mission of the game. From the actual narrative to the marketing, a lot was done to highlight the seriousness of the term "Suicide Mission." Well, BioWare certainly stayed true to their word as it is very possible to not only get your whole squad killed, but your Shepard as well. Fortuantely, with a little know-how mixed with some common sense, it's not that hard to get everyone out alive. However, if you're lacking either ofthose two things, I've got you covered.
The absolute first thing that you should do is upgrade the Normandy. The game doesn't really give you definitive hints towards this, so it's likely that a lot of people overlook it. Each squad member (minus Kasumi and Zaeed) will give you an upgrade of some sort. All of them will benefit you in some way, but there are three that you absolutely need to research in order to ensure everyone's survival.
Ship ArmorFrom Who: Jacob
By either completing Jacob's loyalty mission or asking him about [UPGRADES] under the "Investigate" option, you'll have a chance to research Advanced Plating for the Normandy. As long as you do this, nobody in your squad will die during the armor check part of the cutscene. If you haven't upgraded, Jack will always die.
Kinetic BarriersFrom Who: Tali
By either completing Tali's loyalty mission or asking her about [UPGRADES] under the "Investigate" option, you'll have a chance to research the Upgraded Kinetic Barriers for the Normandy. As long as you do this, nobody in your squad will die during the shield check part of the cutscene. If you fail to do so, you'll lose a squadmate starting with the first non-loyal one in this order: Kasumi, Legion, Tali, Thane, Garrus, Zaeed, Grunt. (If all are loyal and you failed to upgrade the shields, you'll always lose Kasumi or Legion assuming you don't have the Kasumi DLC).
Thanix CannonFrom Who: Garrus
By either completing Garrus' loyalty mission or asking him about [UPGRADES] under the "Investigate" option, you'll have a chance to research the Thanix Cannon upgrade for the Normandy. As long as you do this, nobody in your squad will die during the weapons check part of the cutscene. If you fail to do so, you'll lose a squadmate starting with the first non-loyal one in this order: Thane, Garrus, Zaeed, Grunt, Jack, Samara/Morinth. (If all are loyal and you failed to upgrade the shields, you'll always lose Thane).
The next thing you need to do is secure everybody's loyalty by completing their respective missions. I'll literally go through these one by one just in case you're wondering about any variables that the missions may contain.
IMPORTANT: Once you gain the freedom to do loyalty missions and what not, you'll eventually have the option to get the Reaper IFF from the Derelict Reaper. Make sure you do this LAST. It's important to have every mission completed, then do the Derelict Reaper, then do Legion's Loyalty. Doing this should force the "Collector" scene after Legion's loyalty. It's important to go straight into the Omega-4 after this scene to ensure your crew's survival.
Miranda – Simply completing her mission will secure her loyalty, regardless of any decisions made during it.
Jacob – Simply completing his mission will secure his loyalty, regardless of any decisions made during it.
Jack - Simply completing her mission will secure her loyalty, regardless of any decisions made during it.
Grunt - Simply completing his mission will secure his loyalty, regardless of any decisions made during it.
Thane – If you fail to stop Kolyat from murdering Talid, then you will NOT secure Thane's loyalty.
Garrus – Even if you warn Sidonis, you'll still earn Garrus' loyalty after a chat between him and Sidonis.
Tali – Only if you present the evidence to the Admiralty Board will you not gain her loyalty. This doesn't hinge on whether or not she's exiled.
Samara – If you let Morinth escape, you won't gain Samara's loyalty. This is simple by just following the left side of the dialogue wheel when you're talking with Morinth privately. Alternatively, if you have a high enough Paragon/Renegade score, you can kill Samara and recruit Morinth instead. Doing this will instantly secure her loyalty.
Mordin - Simply completing his mission will secure his loyalty, regardless of any decisions made during it.
Legion - Simply completing his mission will secure his loyalty, regardless of any decisions made during it.
Zaeed – If you let Vido get away by rescuing the workers, you can still get Zaeed's loyalty through a Paragon check. Alternitavely, you can leave Zaeed to die on Zorya (lol).
Kasumi - Simply completing her mission will secure her loyalty, regardless of any decisions made during it.
In two different instances, there will be a confrontation between two members of your squad upon securing loyalty for both of them.
After gaining both Jack and Miranda's loyalty, they'll have a squabble in Miranda's office. You'll need to meet a fairly high Paragon/Renegade check in order to secure both of their loyalties. It's also important to note that the system in place isn't necessarily how FULL your morality bar is, as compared to how many possible points you have at any given time. Still, if you aren't able to secure both of their loyalties, it's a much smarter option to side with Miranda and retain her loyalty for the Suicide Mission. It is possible to regain Jack's loyalty by visiting her on the Normandy, but it requires an EXTREMELY high amount of Renegade/Paragon points.
The other fight will happen once you secure Legion's loyalty, which should be the last mission you do. By this point you should have accrued enough Paragon or Renegade to successfully gain this check. If you still manage to fail it, it's more beneficial to side with Tali. I'll detail it later, but holding Tali's loyalty will probably go further than Legion's assuming you don't take Legion with you to the final battle.
As soon as you land on the Collector Base, you'll start yourself towards the climax of the game where you're going to be forced to make a wave of choices all of which have some hand in your squad's fate.
Tech Specialist: Either A loyal Kasumi, A loyal Tali, A loyal Legion.
Fire Team Leader: Either A loyal Garrus, A loyal Miranda, A loyal Jacob.
The first part of the Suicide Mission revolves around getting a specialist through a ventilation shaft to open a door for the team. Assuming they're loyal, any three of the names mentioned above will work as your choice for the specialist. The next decision revolves around a fire team leader for the other squad. Like the Tech Specialist, as long as they're loyal, either Garrus, Miranda, or Jacob will do. If you followed all of the above instructions, this should go off without a hitch and nobody should die. Messing up either of the two options will always result in the death of the Tech Specialist.
The Biotic Shield, Diversion Team, and Escort
Biotic Shield: Either a loyal Samara/Morinth or a loyal Jack.
Diversion Team Leader: Either a loyal Garrus, a loyal Miranda, or a loyal Jacob.
The Escort: Any loyal party member, although Mordin is the best choice.
The second part revolves around the biotic escort taking Shepard and the team to the heart of the station. As long as you take a loyal Samara/Morinth or a loyal Jack, nobody will die here. If you take the wrong person or they're not loyal, a random member of your two-person party will sacrifice him or herself to save Shepard. Fire team wise, as long as it's one of the above and they're loyal, they'll be fine. Otherwise, the Leader will take a bullet to the stomach and die. You'll also need to send someone to escort the rest of your crew back. As I said, as long as this person was loyal, both they and the crew will all survive. However, for reasons I'm going to detail in the next section, Mordin is the best choice for this job.
Hold the Line, Conclusion
The finale of the Suicide Mission doesn't really have any choices other than what you choose to do with the base. The only thing you need to be conscious of is who you take with you to the final battle. As long as they're loyal, they'll survive the final battle and you should be a-OK. The remaining squad members will be left behind to "hold the line." This is the only ambiguous spot of the game as their survival hinges on an undisclosed "rating" assigned to each squad member. If you sent Mordin as your escort and you take Tali with you to the final battle, you should have everyone survive no problem. Otherwise, they'll start to die in this order: Mordin, Tali, Kasumi, Jack, Miranda, Jacob, Garrus, Samara/Morinth, Legion, Thane, Zaeed, Grunt. That being said, as long as you've secured everyone's loyalty, this shouldn't be a huge issue. I've had Jack disloyal at the ending before and she survived the "hold the line" section, so it's definitely the most random of all the sections. Should anyone die, the camera will pan over their corpse when you're making your final run back to the Normandy.
Assuming you've followed all of the above, you should finish the Suicide Mission with everyone intact. This will net you the No One Left Behind achievement and have you set for a more enjoyable experience in Mass Effect 3.