If you stay where you are until you absolutely cannot live there any longer, you might well be in a crisis and have very little time to figure out where to go and not be able to make as good a decision as you could now. Or not have good choices available.
There is a window of time for moving to any kind of facility. A progressive senior living facility is absolutely the best, since you stay in the same facility, sometimes even in the same unit, depending how it is designed. Thinking in terms of "if/when something happens to either one of us, just move on to a nursing home" is essentially apocalyptic thinking. To stay where you are until something catastrophic happens and the only choice is a nursing home, strikes me as not a very good choice. Independent/assisted living facilities can be remarkable.
I have not lived in one, but at one point I researched them for my mother. I actually found a great place for her, but then she suddenly died, which was sad, but okay. More recently I looked at several for my younger brother. His situation is more complicated and not relevant here. However, I have long since decided that some day I will probably find a progressive care facility and move in. For one thing, at some point I won't want the responsibility of home ownership. For another, I wouldn't expect my only son to take care of me in my dotage. Right now I'm only 72 years old, in annoyingly good health, take no medications, still drive a stick shift car. And even if I remain in excellent health, never take medications, at some point I won't want to be driving any more. Of course, there's always Uber or Lyft or the excellent senior van in my city. But handling the upkeep on my little home, meh. Even now I'm not sure I want to be bothered. The main drawback is that the cost of senior living is going to be almost all of my current income. That's a personal problem that I sincerely hope you don't have. However, down the road, I could simply start spending down what I have to stay in such a place. Again, a personal problem that I will eventually solve.
I hope this is somewhat helpful. 
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