This is a very difficult point for all dog owners to address. Especially, if the dog is a loving pet and not a working dog. At the very least, they can bark at intruders and a good way to gauge the current environment. An unsettled dog can be a very good source of intelligence.
Trying to address dog food would be a pain, so I agree with Yote that the dog would eat what we eat, better yet, hunt its own within a secure area.
Ok, here we go... All this would be very difficult for my 14yr old lab/Sheppard, who has seen her better days. Not sure what I would do with her... Hard to think about really. I'm having a hard time trying to think about putting her down, let alone expecting her to survive in an unstable environment.
In all honesty, if mobility was a necessity and considering her deteriorating stage as it is now, I would ask a friend/neighbor to put her down. I certainly couldn't do it... ugh. I need another cup of coffee. Cheers.