Nobody gets left behind. That was my XCOM: Enemy Unknown rule and it was a rule that I adhered to in almost every one of the hundreds of missions I oversaw. If a squad fell in combat, they fell side by side.
XCOM 2 [official site] has made me break my one rule. Repeatedly. Deviously. Tragically. It’s hard as nails, and superbly distorts the tactics and strategies that were successful in its predecessor. I’m smitten.