Luckily, the tentacle can't reach very far out of the room, so they're able to escape unharmed! It does hit some walls in its pursuit, so some debris falls from the roof as the whole structure shakes, locking one of their paths (the one they came in from).

They do still have a chance to get out of the place, even if one way is closed. There's a hole now where the roof collapsed. Or they can use one of the other, unexplored paths with chances of still making it to the 'something positive' or just more tentacle.