After you complete the quest for the pumpkin hat the only way back in is to,

1. Join a game in progress(more likely boss is dead)
2. Pay the skeleton 200 gold!!(boss is dead again)

Here the problem, you pay the 200 gold to get back in and you end up being in a room were the boss is defeated!! 200 gold down the drain.

Devs please make the boss respawn or make it to were if you do pay 200 gold, you are given a new room.