I'm seeing a lot of bullshit on all these threads from people who are doing the whole "fake bravery about how they would just be euthanized" in this situation, and how life isn't worth living if you're demented, etc.
Here's how life goes for a demented person close to me:
A "fulfilling life" with dementia isn't that different from one without. You wake up, someone makes you a nice meal, you read the papers, shuffle around a bit, get helped to take a shower and dress, watch a movie (which you won't really take in, but it's some nice pictures), get a call from your daughter (who either lives down the road or thousands of miles away, depending on what you're remembering today), etc. On some days your carers will take you for a drive to look at the ocean, or out to a dinner.
You might dream that you went on an exciting adventure down the California coast and tell everyone about it; surprising that an 80-year-old man who can't walk unaided can take a sailboat out by himself. Everyone you talk to will enjoy your story and no-one will try to tell you that you are deluded.
Some days will be better than others, which is the same for anyone.
That's 24 hour home care - and it's not cheap. Neither is living at a facility at this stage. Often the money spent on medical heroics would be better spent on quality of life. Of course, packing folks off to a facility is necessary for some (in this case, we're talking about outright home ownership plus a modest level of wealth). And then a lot of other people frankly want to put hands on grandpa/grandma's money and/or house which is tricky if they are still living in it.