Had several conversations with people in the past couple days about the move to C-USA in 2013. My understanding is that the Sun Belt buyout is not the biggest hurdle. FAU has pretty much decided it will pay the fee, but lawyers are involved in an attempt to get that fee as low as possible. The buyout rules have some inconsistencies and that is what is being debated.
The more problematic aspect appears to be making all the schedules work. A little bit of juggling will have to happen to make everything work. This should not be that big of a problem, but it's one of those things that takes a little time because there are so many schools involved. And it's not just FAU's schedule, it's also MTSU's. My understanding is that C-USA doesn't want one without the other.
Right now, I'd say it's extremely likely that FAU will play in C-USA in 2013. MTSU, FAU and C-USA really want it to happen, and I believe the Sun Belt doesn't have the power to stop it from happening.