When you work in a multi-billion dollar business, and you are a multi-million dollar investment, there isn't much room for excuses. Mental illness or not, this is a results-based business, and DeBrusk isn't cutting it.
While it may sound harsh, he has guaranteed money; it doesn't matter if he plays in Boston, Providence, or another franchise. While it might be sad for him to leave Boston, that's what a seven-figure salary covers.
I think you can sympathise with what, if anything, DeBrusk is suffering from while at the same time acknowledge he hasn't performed well enough and the team should move on. Sometimes business relationships don't work out, and it isn't working out for both parties.
If they go their separate ways, the Bruins think they found someone better, and DeBrusk gets paid - nobody loses here. Nevertheless, if he is suffering from some issues, I hope he gets the help and support he needs, but the Bruins supporting his hockey career is over.