I don't understand why you feel responsible to prop him up. He may indeed have problems but hiding behind someone is a good way to never get the problems addressed and possibly helped. I know that he many need the money, but, if he is no longer able to actually earn it, then, since this is Canada you're talking about, I'm sure that there are a significant number of support systems in place to help him physically, emotionally and financially.
If what you say is true and he is in early stages of dementia or Alzheimer's, he needs to get that problem addressed and the sooner the better. If, on the other hand, he is using his age to not fully participate in his career and is using you to make his life easier, (btw, I don't think that is the case here) then he needs to be shown the door. I'm sure that if the first is the case, then he is aware of it, but denial seems to be his friend at the moment. It's scary when you no longer have the clear thinking ability that was, perhaps, once a solid asset.
It may be a case of not wanting to kick him in the teeth while he is down, but, if what you say is true, there is no coming back up, there still is a long way to drop and that drop will be a lot faster without help and planning while that function is still at least possible. There is no easy solution to this problem. It seem that you have an emotional connection with him, and that makes any action difficult, but, sometime tough choices have to be made for their own good.
By the sound of things, he will not be happy with anything other then being left alone to do whatever he wants, good or bad. He will be mad when you try to help, so that leaves you between a rock and a hard place. The problem is yours only by association, the problem is his, you cannot fix it with bandaids. Covering up the problem without treatment will not fix it.
Since you are hampered by the "boss" that doesn't want to address the situation unless forced, a situation that no manager should ever put there in employees in, there isn't a lot you can do other then express your opinion and let the management decide the outcome. I would continue to, not complain so much, as continue to inform the boss about what is happening. At some point in time the boss has to realize and take action concerning what is best for the company.
I know what you mean.
I thought the music in Her deserved some award recognition over Let it Go and Gravity's score.
) Whatever. They'll get over it. 
