Completely fine compared to other hand/finger injuries.
After a week, or so, of avoiding dropping my pinky whatsoever, I started doing very low intensity 3 finger drags at the start of my climbing sessions, either with feet on the ground still, or doing pick ups with 3-10 kg, and slowly built it up from there.
It didn't really affect my general climbing too much as it was fairly easy to continue climbing on "safe" holds and just being a bit more reserved.
edit: if it is a lumbrical sprain, once it is healed up, I'd recommend your friend does some proper open handed fingerboarding to prevent this happening again. Shamefully, it took me 3 separate injuries to finally get the message that I needed to dedicate some serious effort towards training it.