Please lets see what came apart, I sounds like the RRS Foot slipped of the RRS lens collar, nothing broke as far as I read.
Just not tightened hard enough and the little 'lock' leaver and the RRS lens collar got a small push form something and let go,,, User error I'm afraid,,, be careful how you state it for the insurance
Sorry about that Chris - I'm afraid the D810 is a write off, They will have to change the whole body frame and mirrorbox and that's more work and parts than a new camera,,,