Ok, I went through older saves of the same terror mission and I was able to pointout the moment, when the problems start. One moment, I can finnish the mission without any crash and then, when I shoot down a cyberdisc, it blows up and takes with it a civilian and an alien (sectoid soldier). And then, every time I try to end the mission, game crashes.
I've been experimenting with the saves, but so far no success.