Should I let my husband with dementia go ahead with his plans to organize an ALZ Walk?

The last two years, since he was diagnosed, we have walked for the cure. We formed a team, I worked my fanny off organizing bake sales, rummage sales, keeping track of donations, etc. from other sources. After last year, it became too much for me to think about doing, with all the day to day stuff I have to deal with now that he has declined almost half from what he was last year.

We had the discussion, and I told him I couldn't handle it this year. Yesterday he was looking at the calendar, trying to find October (which I had to find for him) He said he is going to do a walk just like last year. If I didn't want to do it, then he would do it himself. I realize he has no memory of our previous discussions, and may not remember what he said yesterday.

Of course, even tho he thinks he is, he is not capable of thinking of two things at once, let alone doing this. He loves the attention he got from doing the walk and raising funds etc. He doesn't comprehend that others did the work.

Do I cave in and try to do it again, even tho I am already exhausted, or let him go ahead and find out it is not possible?