After making the jump through the Omega-4 Relay, there will be three checks against the Normandy: the Armor, Shield, and Cannon. These can be researched throughout the game and not having these upgrades can have a devastating outcome, the consequences of which can be seen below.
Choice: Upgrade Armor or Not
The upgrades can be made at the upgrade terminal on the Normandy, and the Armor check will be dependent on whether you upgraded it or not. The outcome is as follows:
The research project for the Armor can be obtained by talking to Tali, after completing her Loyalty mission: Treason; it will set you back 15,000 Palladium.
Choice: Upgrade Shield or Not
The Shield check is determined on whether you upgraded your Shields. This has devastating consequences, resulting in you losing a squad member.
If the Shields have been upgraded, nobody will die.
If you didn’t upgrade the Shields, one member of your squad will die.
There is a priority system for this, which according to tests, is determined by who is present when the Tantalus Drive overloads. The order of which squad member dies are as follows:
Kasumi > Legion > Tali > Thane > Garrus > Zaeed > Grunt.
The reasoning behind this is Kasumi and Legion are optional characters, and by bringing them aboard the Normandy, it automatically puts them first in the death list but if you didn’t recruit them, Tali will be in the Drive Core Room and die instead.
The research project for the Shield can be obtained by talking to Jacob, after his Loyalty mission: The Gift of Greatness; it will set you back 15,000 Palladium.
Choice: Upgrade Cannon or Not
The last part of the check is whether you purchased the Thanix Cannon for the Normandy. Same as the Shield check, a squad member will die if you don’t purchase the upgrade, and once again, there is a priority system, which is as follows:
Thane > Garrus > Zaeed > Grunt > Jack > Samara or Morinth (depending on who you chose).
If you do purchase the Cannon, nobody will die.
The research project for the Thanix Cannon can be obtained after completing Garrus’s Loyalty mission: Eye for an Eye; it will set you back 15,000 Palladium.