my first thought is: why did you get an MRI of your hip if you are asymptomatic? So it seems you must have some symptoms!?
To your questions: I don’t know your MRI and x-ray, but FAI is a risk factor for osteoarthritis. So your orthopaedics are making their recommendation for a reason. But is anyone of them an athlete? As you love beeing in the mountains, I would not stop that. But monitor your symptoms closely.
There are also some conservative treatment options. I would recommend to look for a good physiotherapist, where you can get regular appointments and a good strenghtening program.
Moreover there are surgical options for FAI. A hip replacement shouldn’t be the first (and last) step. These other surgical procedures have good return rates to sport. And even with a new hip long days in the mountains are possible.
I know someone who want’s to run 50km with 2 replaced knees. He is a bit crazy, but I’m sure he can do it!;-)
Hope that helps!?