I got the name from @samccone, so maybe he should comment with his thoughts.

I agree that it would make sense to pick a naming scheme that (at least, eventually) might be consistent across the project.  Since we don't need to specify that it's a `region` event here (as the context is that of the `Region`), I think `before:remove` makes more sense than `before:region:remove` in your list above.  Witness `show` versus `show:view`, etc.

I do find that `destroy()` is a common name elsewhere for a method that prepares an object for cleanup.  If `RegionManager` will (soon) receive a `destroyRegion()`, then I'd say let's name it `before:destroy`.  Otherwise, I vote for `before:remove`.