Last year when I had not had my societies long I was moving the cage, accidentally hit it against a table and (gasp) dropped it. Birds and all the stuff in the cage crashed into a corner in a heap. One bird was amazingly uninjured, but Pippin lost flight feathers on one wing like yours apparently has. He was unable to fly until he grew them back. It was months, because he didn't regrow them until late July/early August, which appears to be the usual molt time since all of them molted at that time this year. I don't know if that is normal, or there was another reason he took so long to regrow them. Maybe yours will be luckier. I wish I had seen this post earlier - I could have at least have shared this experience with you.
I think he should be ok with your other bird. I never separated Pippin, but made sure there were plenty of perches spaced closely enough that he could get around without having to actually fly - he sort of hop/flew from perch to perch and became almost as good as a budgie at moving along on the sides of the cage. For perch spacing a little trial and error will show what he is comfortable with. He will definitely be happier back with Ruby.
If you are going to be ordering Feather Fast, you might also get Miracle Meal to try if it's available. My societies love it - I just feed it dry in a treat cup and they flock to it. Here's a link at one place it's available so you can see a description:
http://www.ladygouldianfinch.com/produc ... lemeal.php
Good luck with Tom. I'm sure he will be fine. Societies are wonderful birds - but I'm sure you know that.