Oh yes I was thinking about that too... your idea works, if that's what you'd like to do with him? House of M is actually really vague about what happened to Professor X - his mind was connected to Wanda's when she activated her spell, so she was able to use him because of that. In the AU itself there was a grave for him, but when Emma and Cloak checked it out, it was empty. He was never shown while it was happening, and afterwards he disappeared. I'm not sure if/when they found him after that. Needless to say, following House of M exactly with Billy and Hisoka would be a bad idea for both of them xD

I like the idea of Billy hiding him away somewhere - heck, even keep him around in the spare room of his and Teddy's apartment, since no one goes there - and checking on him every day to see how the perfect world is going. Once the spell wears off and everyone snaps out of it, Hisoka could either be rescued or just let himself out. Or of course I'm open to ideas if you have any!