I also like “the bubble.” It was one of the reasons I became really engaged in Concordia, for example. Coming up with Alistair’s cat was a happy bonus to that. That cat was a built-in bubble for me, because I could just make up vignettes/short stories about him. >.>
As to the “burst bubble” status, so to speak? I don’t think I could even opine upon this, to be honest, and I’d be preaching to the choir and/or broken-recording what’s already been said in this thread. The people that will stay, will stay, and for their own reasons: plot involvement, friends they enjoy IC and OOC interactions with, bar rp, and so on.
Personally, I don’t think a game should “entice” people into playing via anything other than the theme and any game-specific features/rules its runner(s) want to have.
In other words, the game should speak for itself.