Hi Ann,
I was diagnosed as a stage II. I'm really wondering why your dad didn't get 5FU at the same time as the radiation since that is the "standard of care". I had the 5FU continuous infusion 24/7 for six weeks at the same time as 28 sessions of radiaiton. I also got the mouth sores and the onc. decreased the dose and they got better. I was a little tired, a little nauseous but they have wonderful antiemetics (for nausea) drugs and so that wasn't an issue. My cancer was Mucinous adenocarcinoma which sounds like what your dad had. Did the path report after surgery say if his margins were clear? He really needs to have the chemo in case there is even one microscopic cancer cell they missed so it can be killed off. There's never any guarantees but I would do what ever it takes so if it does come back you aren't saying to yourself "what if".
Good LUck!
Terry