Keep them busy
Once they have had a bit of recuperation, sign them up for as many activities as possible. Ideally send them away to a camp for a few days where they don't have a second to sit around and mope. Teenagers suffer from the terrible affliction FOMO — the fear of missing out, a constant state of paranoia that their friends are somewhere else having more fun than they are. If you can get a couple of friends to go to a camp or activities holiday then the FOMO horror is reduced. Once out in the great outdoors abseiling down cliffs they will have a great time, even if they won't admit it.