Is it impossible to leave Sun morning?

You should tell the people at the gate when you enter that you need to leave early and beg them for an easier spot to leave. If you can get the right spot, it won't be too hard.

From my experience, parking is a total crapshoot and most of the people working don't care and just usher you in place.

That said, I've left early the past two years when I thought I was trapped both times. Where there's a will, there's a way. Just ask your neighbors kindly if they can possibly move some things around and you'll get out.

Sunday night is easy, in my experience. Lots of folks leave out on Sunday. The above advice still applies, though...try to get parked near the end of a row if you can. Maybe the best thing you can do is try to meet your neighbors as early as possible, hand them a cold one or something, and let them know that you will be bolting on Sunday. It may or may not make the difference, but folks will be much more helpful about protecting your exit strategy if you kill 'em with kindness on the front end.

I've never been in BFE, but from what I've read on here, It sounds like you wouldn't have a problem leaving Sunday morning.