Yes, it's in our will for my brother and SIL to take on our cats if anything happens to us. We also have money set aside for their care (vet bills, for example). When we revised our will, we put it something like "all cats in our possession at the time of our incapacities" or something like that....I forget the exact working; our attorney wrote it up. That way, however many cats we have, they will all go to my brother and SIL. (If anything happens to them before us, my sister said she'd take the furkids....she will not have them go to a shelter.) Five of our 7 are geriatric with four of them being quite elderly at this point, so hopefully we will outlive them (and I know that this is not a good topic for conversation, but it's important).
When we did the will revision, we had five cats. Then came Mollipop, followed by Tabby. My brother told us that maybe we'd better stop as they've never taken care of more than five cats at one time.

We promised to keep things on an even keel for awhile now.
If you do have something in your will and when you have family, friends, whomever, willing to take on the responsibilities of caring for your furkids, I think it's a good idea to set an amount of money aside for their care, especially if you've multiple cats. It helps your caregiver to take good care of your cats. IMO.

Susan, I guess I should add that most of our deceased kitties' ashes are in containers on a shelf in our living room. Because I would like to be cremated when I die and I don't want to even have my ashes buried, I am content just to mix my ashes with the cats' and then scattered in our back yard. Or in a flowerbed. I do not want to be underground. (And yes, I know how silly that sounds.)