If I'm alone in an enclosed area, I let go tuck and roll. If I'm somewhere he can run off and leave me, I try to hang onto the reins, but usually just take the fall if I know it's inevitable. If it's a marginal thing where I'm at a show, and he's only got me a bit out of the tack, sure I'll give it a try before I bail. I've noticed with falling, it's an intrinisic thing. If you think you'll stay on, you usually find a way to make it happen. Once you decide you're coming off, you're coming off.
You just have to see your distance...you don't have to like it.