i'm pretty sure any reasonable and caring person with dementia, if they actually had enough cognitive function, would NEVER want to burden their kids in such a manner. it's one thing on your death bed but another to take care of someone for the rest of their life.
As long as they are taken care of well (not just thrown in some 2nd rate home...at least a place where they specialize in these things), and the family comes and visits them...that should be enough.
when you lose your mind, you pretty much lose your entire existence. it's not the same person you knew/know. your mind and memories are the basis for your identity