This will require total colectomy as it carries a high risk of developing colonic malignancy. By now you must have received your biopsy report. It might show already changes of malignancy or even if not, would suggest you to plan for colectomy- lap or open which ever way you find better. Personally I would suggest laparoscopic method.

Incomplete information..biopsy report??any associated problem..syndromes??genetic association?? If endoscopy method not possible then surgical options available..,need clinical evaluation and opinion from GI surgeon or general surgeon experienced in such type of cases