I'm sorry to hear your finch has a congenital deformity. The good news it that he's a pet and will be cared for rather than a wild bird who wouldn't last 2 weeks.
Mostly likely he won't grow any significant feathers on that wing. I haven't seen the deformity but typically that's what happens. He may get a few feathers that stick out this way and that. Mostly keep a close eye on that wing, watch for any injuries that may happen since it isn't protected. Provide lower perches for him that he can climb his way up. He needs to be perched for the sake of his tail feathers and feet but you don't want him falling too often. If there's a way to add some substrate to cushion the bottom of the cage, that would help too.
We have a Red Tailed Hawk at work that is handicapped due to being hit by a car when she was young. Now she's older and has arthritis as well. We used some indoor/outdoor carpet in her cage. Her perches are only a few inches high but we still want to cushion her a bit. I don't think that's a good choice for the finch though since the bird will want to pick at it with his beak.
thanks for the reply. sadly the finch is in a large aviary and it would not be possible to cushion the floor. i have put some lower perches for him which he does use. its just so sad to see him peering up at the other birds. i have tried him indoors in a cage but he panicked and was hurting himself. the wing is there but the main feathers are missing thats why i was wondering if they may grow when he moults.