[hotpotamus]

You've hit the nail on the head. I also have a childhood hip condition (Perthes disease) that has had me looking at hip replacements since my 20's and having the same fears as your friend.

Looking at pro athletes is sort of instructive; essentially none of them have returned to play after a hip replacement (Bo Jackson kind of, but in limited capacity). A few, most famously Andy Murray, have returned after hip resurfacing, so it's probably about as close to a natural hip as possible, but likely still a bit inferior.