Good luck to them both, hope Matt sorts out whatever the problem is.
Same from me.. best wishes to both
Not trying to 2nd guess what Mullan's personal problems are but Haskell (in his Joe - House of Rugby podcast) touched on the difficult transition a lot of players face when they approach or go into retirement.
Most players have been used to a daily/weekly schedule revolving around training and playing for perhaps over a decade and the difficulty they face when that's taken away.
I'm guessing its similar for someone with a long term injury (especially towards the end of their career) in that the normal routine changes and to some extent the normal goals aren't there.