I think when people wish to play an episode, there are more likely to want to play it from the start, than continue something someone else played half thru. Especially true if items are not set to respawn. You are joining with just a pistol, some of the good pickups might already be gone, and you might still have mobs to deal with.
If I happen to spot my server half way thru the game with no one in it, I usually just reset it manually. This is also a biased decision because I know that upon reaching the end of the episode it's gonna be stuck anyway. So a server on E1M1 has more playtime in it, then a server on E1M6.
Such a feature would workaround the need to code a separate fix for the end of episode situation, but that should really have it's own fix. Main difference being that shouldn't wait for the server to be empty, and the timer should probably be a different value. I'm thinking something like 10 minutes for the former and 30-60 seconds for the latter (depending if it counts at the start or end of the "end text").
A map vote system would also workaround both of the previous ideas.