I suspect that urinating in the house has nothing to do with the dog’s diet. As a senior he is vulnerable to all sorts of things, such as UTIs, struvite (urinalysis will rule out), bladder stones (ultrasound will rule out).
So, I think a call/visit to the vet is in order. I wouldn’t change his food from what a veterinarian that has examined him has recommended. Pancreatitis is a serious condition.
PS: I would see if you can collect a urine sample to take to the vet. A empty prescription pill bottle (clean) will do. You only need a small amount.
