razor343 said:
Mordin, due to some stupid glitch with Mordin dying no matter what you do.
It has nothing to do with any "glitch".
At the end when you take two party members to face the final part of the game (including the human reaper), the squad members remaining back each have a "defender" rating unique to each character (with non-loyal squad members having a significantly lower rating).
If the combined defensive rating (measured in an average i believe) of the left-behind team is too low, then there is a chance that someone dies. This someone will always be the one with the lowest defensive rating, which of all the NPC's happens to be Mordin (if you did all loyalty missions that is, otherwise non-loyal squad members will have a lower rating).
There is actually a chance of him surviving if left behind, if the other characters left behind has a high defensive value (that would be characters like Zaeed, Garrus, Jacob etc. aka. strong fighters). You take some of the stronger ones with you leaving weaker behind, it might go wrong. The entire system is explained here:
http://masseffect.wikia.com/wiki/Suicide_Mission#Suicide_Mission
The sure-fire way to make Mordin survive is to have him escort the Normandys crew back to the ship after you save them (or take him with you for the final part, which in most cases also means that the remaning squad members will have a high enough survival rating to make sure that noone dies).
@ Topic: Jack died on my loyalty Mission (on purpose). I never liked the *****, so according with the link above i posted, all you need to do to make sure she dies is to avoid purchasing the armor upgrade for the Normandy.