You are right to worry, OP, because it is horrible to deal with. My dad died a few years ago, and my mum's health has been deteriorating since then. Earlier this year she moved into a residential care home, as she was no longer able to cope at home - she has both physical and mental health problems, and was recently diagnosed with dementia. She had started wandering out of the house at night.
I hate that she is in a care home at a young age (mid-60s), but it is far less of a worry than her being at home, even though she had carers coming in four times a day as she needed help getting up and dressed, preparing food, and getting to bed (and making sure she took the correct medication).
My sisters and I have all moved away from our home town, and it has been a great strain on all of us - the constant worry, the strain of visiting frequently (at one point one of us would visit every fortnight, despite my sisters having young children), the fact that we needed to deal with mum's finances, sort out any problems with the house (falling apart due to years of neglect), and deal with crisis after crisis.
It is very difficult to have to become the parent and see your mother become the child in the relationship. Five years ago I had never thought that I would need to help my mother have a shower, get dressed, help her change because she had wet herself but the carers hadn't put a pad on that morning... It's horrible, but you do it because you have to.
I've seen several posts on Mumsnet where people have said that they won't expect their children to care for them, they don't want to be a burden, etc. But it's not the care itself that they need to think about - it's the little things, like taking your mum clothes shopping, helping her buy presents for her grandchildren, posting off birthday cards and christmas cards, taking her to doctor's appointments and dentist's appointments, keeping an eye on her finances, arranging repairs to the house, buying new bedsheets when you realise your mum only has one set of double sheets for her bed (despite having enough money to buy more)...
I'm not a saint - I feel very resentful, and angry at my mother even though I know it's not her, but her illnesses that caused her behaviour. It's hard because most of the people I know who are my age (mid-30s) have healthy parents, and perhaps have frail grandparents. Three friends have lost a granparent recently, and while I know they're grieving, I know they won't have dealt with all these issues - their parents will have been the ones dealing with doctors appointments, hospital admissions, being a carer. My friends have had an inheritance from their grandparents, while my mother's house will be sold to pay for care home fees. They have no idea what it's like - in some ways I have more in common with my MIL, who cares for her elderly parents, than my friends.
Practically, you could: make sure your parents are in a home they could stay in with mobility problems (downstairs toilet etc), encourage them to downsize and clear out years of clutter, make sure the house is kept in a good state of repair, be aware of their financial arrangements and think about the future - my parents didn't have a joint account, for example, so when my father died my mum didn't have any income apart from her state pension until his pension was sorted out. I paid for my father's funeral, because he didn't have any savings we could access.
It all sounds horrible, but it would have makes things much easier for me if my sisters and I had done this while my parents were healthy.