I see some good things about this.

a) he's been diagnosed which means that he can get what treatment there is.

b) alzhiemer's progresses very differently among different people - he could go on for years and years with only some short term memory loss.

c) treatment is getting better all the time.

d) he knows what is happenning - and that means to some extent will be able to compensate (at least many Alzhiemer patients are able to in the early stages)