Mushmom can heal herself?

Does the EXP return to no-ones? Because I always hated going into a F/Ps old map and having do to an entire loop and basically get 0 exp...

Nah. There was this one time I was at skeles misting, then I had to leave. Eight hours later, I was surprised that my exact spawn was still there. I still got the full exp off 1 hitting them. Hypothetically, if they had healed, I wouldn't be able to 1 hit them.