They don't get any lives back once they start part 2 though. If you think they are about to get to part 2, leave them with just a few lives left, if you're not confident you can kill them outright.
Generally Loaht's house tends to die in roughly the amount of time it takes to burn through 36 lives (which takes wayyyy too long imo). The AI balance with antags present is definitely a problem lately, and will always favor whichever side has less MMR (so if the raiders are lower than the antag, the map is super easy). Aside from the balance problem being an issue over-all, I feel like the survive timer for part 1 of short fused needs to be way longer. It's only, what, 30-40 seconds? If the antag gets killed during any part of this timer, there's not going to be enough time to finish them considering there is hardly any wardog support at all in part 1, and the map is huge. I'm not sure if I've ever won by killing in part 1 despite burning through all their lives, I believe every team I've fought has lasted through survive and I just stall them until Loaht's house dies. Which takes like 15 minutes, is what it feels like..... we don't get to see how long missions are when the antag wins, so hard to tell.
