One of my elderly uncles was in this position, but he was a bit more responsible about it than your grandfather. His way to solve it was like this: he sold his car at a discount to someone else in the same building on the condition that when he needs transport they'll drive him. It works out well, he only uses it when he absolutely has to and the rest of the time he either walks or has stuff delivered. It was a painful decision for him but in the end it worked out well (and I'm the backup driver but I'm about 100 km away from where he lives so it would always take me at least an hour to get there).