In all three ending options, Shepard is either assimilated or blown up and assumed to be dead. The only ending that Shepard can survive is to choose to destroy the Reapers and have an Effective Military Strength of at least 5000, or 4000 if Anderson was not immediately killed by The Illusive Man. In these circumstances there is an additional scene at the conclusion, showing Shepard is alive and lying in a pile of debris.
At the end of the mission on Rannoch, if Legion/Geth VI is allowed to upload the Reaper code then Tali will commit suicide by throwing herself off a cliff. If you prevent the upload or peace is made between the geth and quarians, Tali returns to join the team onboard the Normandy.
If you speak to Thane in Huerta Memorial Hospital prior to the Cerberus attack on the Citadel, he will be fatally stabbed while defending the salarian councillor from Kai Leng during the attack.
At the conclusion of the Cerberus attack on the Citadel, Udina is shot and killed either by Shepard using the renegade interrupt action or by Ashley/Kaiden.
During the genophage mission on Tuchanka, Kalros the Thresher Maw attacks the convoy and kills Wreav, but only if Wrex has been imported from a previous save. Otherwise Wreav will lead the krogans in Wrex's place.
If you decide not to cure the genophage, Wrex will eventually find out and aggressively confront Shepard. No matter what dialogue options are selected at this point, the outcome will always result in Wrex being shot dead.
After investigating the volus ambassador in the Citadel, Shepard discovers Zaeed and his mercenaries have kidnapped him. Shepard feeds information through the ambassador that makes Zaeed realise he's been tricked, at which point he kills the mercenaries but dies in the process unless his loyalty mission was completed in ME2. If he survives, Zaeed is added as a War Asset.
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