Good that it landed on the rear cap. That absorbed part of the shock, the rest being distributed over the entire mount flange. With no cap on it you could have had a bent mount, plus internal damage.
I was sent a Nikkor 24mm once that had been dropped on it's rear with no cap. It wouldn't focus to infinity anymore, and the baffle was all bent up. Thought if I removed the rear baffle and straightened it, that would solve the problems. Mechanically, it seemed okay after the operation, but when I shot with it I found out the optical block was now out of alignment, making everything on the left side of the image out of focus relative to the image plane. It was hard to see that in the viewfinder, but definitely showed on the prints. I'm still thinking of having it rebuilt because its a somewhat rare early version.
Good luck with yours, Joe, sounds like it has a good design build to take that kind of punishment.
PF