What kind of dog is he? I think if he is a breed that tends to be long-lived that can make a difference in your choices. I would look at many of the alternative treatments. Many have had success with Graviola, Piroxicam or dietary changes/supplements. I will tell you the same others have offered - go the the Bladder Cancer message board and look for the big (600+) thread for Canine Bladder Cancer. Lots of info there, but it does take some time to get through. I try to take some time everyday to look bach through it - I haven't gotten through it all yet.
There are hard choices to make with this disease. Hopefully you have a knowledgable vet who will work with you on alternative treatments. But in the end, you know your dog and you will know in your heart what is best. Love him everyday you have with him.
Connie