Kelly,
My 28 yr old daughter, Heather, has base of tongue cancer and is currently undergoing radiation treatment. I recently started a post about the PEG tube. If you read it, you will know that my daughter just had one placed and she did have some trouble with it. But, just today, she told the dr. that despite the pain, she is still glad that she got it.
In your father's case, it sounds like he desperately needs one. With the pain he already has from the mouth sores and sore throat, I would think that the pain of getting the PEG tube would seem very minor in comparison. And, yes, many people have said it took quite awhile after RAD ended before they had healed enough to start eating regularly. So the fact that his treatment is almost done is not a good reason to not get one.
Also, Heather's pain was caused by the fact that younger people have more muscle in their abdomen. And it is not muscle tone that counts, just muscle (she does not have flat abs by any means. she was actually overweight with a flabby stomach). With your father's age, the PEG tube should not be that difficult.
I would ask the dr. why he feels it isn't necessary. Also, could the fact that your Dad doesn't have insurance be a factor in the drs decision? I would press the issue until you feel comfortable with the result.
Good luck,
Rosemary