I'm not sure if there is or not, but it's something to look into.
Believe it or not, I just had this same talk with our son who lives here with us. (he's 20) and asked him if something happened to his Dad and I would he want to keep Abby and Daisy? He said that of course he would. I reminded him that they require lots of care, grooming, vet visits, special diet, walks, pottying, etc... and I told him who I wanted to have them if he found that it was more than he could handle or if he moved somewhere that he couldn't take them. I suppose I should inform that person too, huh?
I've heard of some folks here leaving a few thousand dollars in their will to the person who cares for their animals.
It is something that needs to be thought about, just as we do with our children.