Growing old with mental illness is a real worry. I think many more people would feel more at peace and experience whatever degree of happiness they can, if they knew they wouldn't have to worry about homelessness or "falling through the cracks" in old age.
I believe in planning whenever possible, but trying not to worry. Here in Canada there are many free services for older people, where care workers or nurses will visit the person's home to help with self care, dietary needs and so on. There are also volunteer services for things like grocery shopping or visits. And finally there are private services for those who can afford them. Many people can remain in their homes unless they become very debilitated mentally or physically.
I think it's a good idea to learn about these things ahead of time in case I ever need them. I'm 52, so maybe when I am 62, or 72.... I hope I never need them!
But in Canada we still have the "interesting" gap when it comes to care homes. Those at the bottom financially get government care homes which are generally better than private here. Those at the top of course can afford the $5,000-per-month luxury retirement villas. Those in the middle.... Well, my mother managed to find a room in an independent-living residence for just over $2,000 per month (which is a real accomplishment as the average rent in that area of the city is about $1800/month) and she gets her room (including bathroom and small kitchen and patio), all meals(!), once weekly cleaning, and some other services. Her pension covers it and leaves her some spending money, and the funds from the sale of her home are in the bank. Of course we would help if she needed it but she is set.
So, it is possible. Remember these prices are Canadian dollars. My mother adores her residence, likes the food, and has made friends with some of her neighbours. The facility does trips for them, arranges transportation to medical appointments, and they have exercise classes and a hairdresser on site.
I hope and pray we all have such good fortune in old age. She's 83 btw