Sad about your loved ones depression following the death of this great boxer who has contributed so to the cure for PD , It is said (an ongoing conversation here) that Michael J.Fox is also feeling defeated by Parkinson's but we must also remember Muhammad Ali & M.J.Fox endured this disease for more then 30 years by my estimate... that is truly incredible !
I am seeing the same downhill changes in my wife's PD after 16 years ,although I was prepared for it all, still it becomes sad at what was taken away ,I try to look forward and not look back .
I would discuss the anger and see if it stems from fear of the unknown ,then perhaps comfort that fear by stating the good accomplishments he has been doing lately on his own .
Good luck,
Mike