A city with less cars is a net positive for mobility impaired people.

It frees space for people (wider sidewalks...), reduce the risks of navigating the streets, and for the ones that have to use a car, there's less traffic and less people stealing dedicated parking spots.

Less cars also means less mobility impaired people. Cars create them through crashes and a lifetime of sedentariness.

Finally, it should be noted that most of the time when someone says "what about mobility impaired people?", when debating reallocating public space to people instead of cars, they are not mobility impaired themselves and don't actually care about them. They just try to guilt shame their opponents to win.