The survival rate of your squadmates depends on who does what during the survival mission. If you pick a good team leader (I suggect either Miranda, Jacob, or Garrus) for the Fire Team the person crawing in the vents will die.
If you are loosing him at the end and heis the only one dead, this is more troublesome. You can send him to escourt the survivors back without problem or keep him in your final squad, if you want him to live. After all, we all want to see him perform Gilbert and Sullivan once more.
Addendum: this is how i got 100% survival rate. Before Suicide mission start: Buy Thanix gun, Cyclonic shielding, and Heavy Plate Armor upgrades for ship.
Tech Specialist: Legion or Tali Fire Team 2: Garrus
Crew retrieved/The Long Walk:
Fire Team 2: Garrus Biotic specialist: Samara/Morinth or Jack Survivor escort: Mordin