I think there might be a more caring way of having this conversation.
Most older couples - I am married to someone who is in their seventies - will talk about how they plan to deal with increasing age, what the surviving partner will do when the other one dies etc. Or even if not much is said, both partners will - or should - be thinking about this. (As your father is doing, though not in a realistic way.'
It would be unusual for someone who didn't drive and wasn't very practical to want to live alone in a large house in a rural area. Though of course somebody who's been left very well off can buy in help, take taxis etc.
So it's hard to know whether your father wants to be sure his widow would be alright.
Obviously if you're only on civil terms with his wife, you don't really know what she's thinking. But in your shoes I might be trying to have a three way conversation, 'How would you manage this big place if one of you were left on your own.'
At which point she might say, 'Oh I think I'd go and join X in Dubai.' Or lovely as it is out here, I'd be tempted to get a flat in London, so I don't have to look after a big house where I can just get the Tube everywhere and go to all the museums.'
Which allows you to say, 'Terrific plan about London Easy for Dubai-son to hop and a plane and for other son to get the train see you. Because of course with my busy job, I'll be no use whatsoever But it'd be nice to meet up for coffee in the Tate once in a while.'