The 300 PF apparently survived with just a few minor scratches. Managed to get the extra camera mount off it as well (the one that was ripped off the Df body). The coffee stains on its rear element went away with some soap on a chamoise cloth.
It probably was saved by (1) the hood being stored reversed so effectively would act as a cushion and shock absorber and (2) the lens tripod collar + Arca plate added even more protection. Yesterday, I ran a comprehensive test session with the 300 PF on my second Df, checking alignment, proper focusing, VR functionality in 'Normal' mode, and consistency of exposures ('E' aperture). All results looked good.
As all main Nikon techs are on their summer vacation at present, I have to wait at least 2 weeks to get the camera repaired. I wonder whether the designated shearing zone for impact has protected the camera's mirror chamber from coming out of alignment. Everything else with the camera seems to work: it turns on and off, shows previews and menus, and I can trip the shutter. The massive "L" plate must - again - have acted as a protection to the vulnerable camera body.