I disagree, they all knew what the stakes were, Ellie and Tommy were probably prepared for it to be a one way trip. Then they already agreed that their revenge was sorted. "It's going to have to be enough." Tommy's just mad Abby ruined her shit. The story is about learning to forgive. The goal is (imho) to make Ellie/the player forgive Abby. You can hate her all you want, and whether the game succeeds is up for debate. It wasn't that she just decided revenge was bad at the end, you don't just stop wanting revenge in the span of a few seconds. It was that she realized, "I don't have to do this. It won't bring Joel back. It won't get rid of my PTSD. I'm about to do to to Lev, what Abby did to me, what Joel did to Abby."