You mean "dedicated servers" ? That's already a thing :v

Your friend hostet a p2p game so the world will only be available when that friend is playing it or at least lets the game run, ofc they can go afk.

The other way to host a game is the dedicated server. Either at home, a server you own/rent or as a paid service.

Think your going after if the host state could be transferable. But the original host would still have to be online for that to happen.

I have not really seen that being possible in other games yet, but does sound like a nice idea.

How the ♥♥♥♥ do you want this to be possible? Having a ghost magicle keep the server running while his pc go offline ?
Just rent a server on a hosting company and 10 players can play when ever they want...