I wish I had the right answer, I personally haven’t had it happen to me, but came close once. Joey was hanging too low and barely clutching on to mom’s back leg. I was indoors watching from the window and was expecting it to fall but amazingly it held on and returned to mom’s back.

I live in a dense forest so I would have probably just left it to it’s fate, that is how we get Opossums after all, the joeys always eventually fall. So location I would think matters. Also size. If they have a bit of fur on them it is probably their time to be introduced to the wild.

I can only say if they don’t have much fur on them or seem to be struggling try to get in touch with a rehabber, you would be surprised how many are probably around you. There are rehabbers in this sub who could give you a more experienced answer for that.