After infiltrating the Collector Base, you’ll have more choices to make which will determine the survival of your squad. You and your squad will gather in the briefing room of the Normandy, EDI will scan the Collector Base looking for weak points, and the main control center will be said weak point. With only two ways to get in there, you’ll be forced to make some choices. This is part of the Stop the Collectors: Defeat the Collectors mission.
Choice: Vent Specialist
The first choice you’ll have to make is who to send in the thermal vent; you’ll have to send a tech specialist. The specialist will die if they’re not loyal to you. Here is a list of ideal candidates for the job:
Ideal - Loyal Kasumi, Loyal Legion, or Loyal Tali
Non Ideal - Anyone else, including a non loyal Kasumi, Legion or Tali.
To make sure you have a loyal Kasumu/Legion/Tali, complete their Loyalty missions.
Once you’ve made the first choice, Miranda will say you (Shepard) will lead one squad, but you’ll need someone else to lead the second. She’ll volunteer, but you can choose anyone. If you fail any of these checks, your vent specialist will die.
Ideal - Loyal Miranda, Loyal Jacob, or Loyal Garrus.
Non Ideal - Anyone else, including a non loyal Miranda, Jacob or Garrus.