I am arguably the only person available to help with and oversee my spouse's health, living situation, and course of life in general. I am her HPOA and PPOA. She has no close younger relatives that I could see stepping in to help her should I pass away. She is in a supportive living facility now and exhibits signs of Vascular Dementia as a result of 14 TIAs/mini-strokes.
Take good care of yourself anyway, and don't let this possibility add to your stress levels. If she's already well looked after it's reasonable to expect that to continue - nothing appalling will happen to her.
I saw an Elder Care Attorney (was seeing one anyway due to the Guardianship I had to have..long story) I had a Will done for myself with a Special Needs Trust that would provide for him if something happened to me.
A set up like that would care for her in the event of your death or if you became incapacitated. You should have a POA, someone to act on your behalf if it came to that. You can appoint a friend, relative or the lawyer can handle that.
If there is nothing like that set up and there are no relatives she would become a Ward of the State and any monies from your estate would be used for her care with the State having control over the money and where she is placed. (the state could move her to another facility if they chose to.)