I know many rescue people have fostered seniors, often to the end, bringing them in with their younger resident dogs. I know Dharma'sMom fostered a senior. You could PM her. Hopefully, someone with this experience will chime in soon.
Bless you for considering rescuing a senior. Seniors are the best.
Natty Boh 6-27-12
Annie 1998 - 8-2-12 RIP