I gave up on the last mission after it bugged out a couple times. Not only that but once you get to the final mission, even on Ironman you can fail it and still retry it again. Once some enemies didn't spawn and another my sniper was stuck two rooms back on the jetpack because it ran out of fuel but she wouldn't land because the ground was "blocked", in the middle of an empty room no-less. The final enemy immediately possessed my psionic and best assault soldier and after the squad was dead the sniper had the mission un-winnable. Loading the game just put me in the same spot.
Assassin's Creed did something similar at the very end. I quit out and when I loaded I was in an area that was invisibly walled in. I wonder if that's why I have a habit now of not finishing games with about a half hour left.
