I've dealt with it a long time ago on an old Shepherd, but again, not on a Corgi. Kidney failure can often be slowed a bit by diet and giving subcutanious fluids to the dog, and some dogs can live a long time with good in-home care and regulation and getting their bloodwork checked regularly.
The bit about his hind legs concerns me, though, did your vet diagnose DM (Degenerative myelopathy) or anything else?
If not, does he just have a hard time getting up off the floor after he's been resting, or are his nails (or even toes) on the back paws getting dragged and worn? Is he on any pain medication?