The thing is you don't know until it happens.
When I was young I couldn't imagine being in my late 60s, deaf in one ear dealing with the after effects of prostate cancer but here I am. When I was married to my first wife the idea that in her early 40s she'd be diagnosed with aggressive Multiple Sclerosis and would be dead when she was 50 would have been unimaginable. Even in the early days if you'd told me the extent of personal care I would have to provide towards the end I would have said that it was something I couldn't do but slowly without realising that's what I did. Living here in Thailand wasn't something I would have thought possible.
I think we just grow with the situation we find ourselves in. Sometimes that may get too much and maybe we'll want to give up but I don't think you can make that decision until the time arrives.