Trust me, it really isn't a lot of fun. I have a very similar body type to Tadgh - very flexible - and have dislocated both kneecaps in the past. Probably the most painful thing that has ever happened in my life and I've copped a few knocks.
Unfortunately there isn't a lot he can do to prevent it happening, you can strengthen the muscles around the knee but the joint is naturally loose in some people so it could well happen again. There is major surgery you can get but there is a very long recovery period and it would rule him out for the season. In terms of recovery the main issue is trauma to the area and confidence - it sometimes takes a while to regain confidence in your knee and run and turn at full pace. Because he's had the injury before that would have helped him return earlier.
Hope that helps a bit
