Probably find another promotion site to promote my own forum at. Shouldn't be too hard there are loads of them out there these days. Although I probably would be a bit upset at first as I currently get most of, if not all my traffic, from FP.
I would just move on, really. If the owner and staff were to wish to share what happened to the place, that's their business. If it was something personal that went on that nobody wishes to really talk about, then it's none of our business. As long as they sent out an email or whatever informing us of the pending closure if this were to ever actually happen, that's really all that matters. People close their sites for different reasons, and nine times out of ten, those reasons really aren't any of the members' business. If they just said that they closed this site for personal reasons, then that would be the reason we'd have to accept. It wouldn't do any good to pester it out of them as to why they actually closed the forum.