Wow this is certainly an extreme situation. I thought that once they remove the spinchter, he would have to have a bag for the rest of his life, but I am not up-to-date ont his. If they remove his rectum, how would he ever not require the colostomy bag?
I have met a guy who had his entire colon removed and they made a "colon" using two lengths of small intestine split down the middle and stapled together lengthwise. He said that after things settled down everything worked OK.
My concern, however, is that the substitute colon would not have the portal vein system and the liver would no longer provide the necessary detox of the bowel. I guess that he would almost certainly have longer-term health issues due to this missing pice of anatomy. On the otherhand, he won't have any long-term issues if the cancer is not resolved.
I would still get that second opinion. Perhaps a visit to a good cancer center.