That's awesome, cat level longevity.

How would they fare as indoor, backyard dogs taken for twice daily sedate walks though?

My personal (probably unpopular) opinion is that a lot of inner city people should not have the dogs they have - who need to be able to run around at all times, not just waste away.

It's also why I don't have a dog, for exactly this reason - I don't live in the country, with enough free space around.