I'm not sure if a similar mod idea has ever been posted, but it seems like a pretty simple alteration to the game, albeit I would have no idea how to do it myself. Basically, my idea is to have a mod that can end a mission in late game, even if you have an alien under mind control once you complete your mission objectives. Once the mission ends, that alien is then presumed killed by your squad, and their corpse and weapon fragments are added to the list of retrieved items. But I would also like to propose a second option. If one of your soldiers has an Arc Thrower that still has some enough charges left once the mission ends, that alien will be taken captive instead of killed. It would make Mind Control a little less annoying to use, especially towards the end of a mission where you have to dedicate an entire turn to blowing up your controlled alien before they have a chance to attack you again.