Hiking a New Trail

My husband, Abe, was diagnosed about 3 years ago with atypical dementia.  He is on medcation (Aricept) and his deterioration has been show.  He has had to stop driving, and he relies on me more and more for day to day decisions and help remembering where things are what we are doing, etc.  Wwe still are able to go out hiking with small groups of friends, but larger groups don't seem to work well.  We also play Bridge, and here I can see the gradual decline clearly as he looses the ablility to use conventions, forgets what is trump and works to set up a suit only to forget he has done so.  So hard to watch!  I don't know if I should let him continiue playing until he becomes so frustrated that he throws the cards down, or intervene.  It seems like he is not too aware of his declining skills.