It was pretty much the same with ours. The only thing the cancer was doing was obstructing the outlet of her bladder, making it difficult for her to pee. We knew eventually it would become too much of a problem to keep going, despite the fact that she was still very energetic, not in pain, and enjoying life, but we didn't know how long it would take.
Eventually her life was a complete preoccupation with peeing, to the point where she was barely sleeping much at night, just going out hour after hour. When she started leaking, we knew it was time.
We had an in-home vet come and do the euthanasia, so she could be at home in her yard when she left us. That really helped, I think.