If you have your colon removed how long can you live for?

Same as with it: It depends why you had it removed. If it was for diverticulitis or some other benign disorder, there is no reason you cannot live as long as you would have lived with it. Of course, if it were for cancer, the answer depends on the cancer's stage.

Decades!: While it is nice to have the whole colon, you can survive without it just fine. The colon absorbs water, so you may have more runny or liquid stools, but otherwise, you should not have any decrease in life span -- although it depends why it was removed? (for cancer: there is a risk of recurrence; for ibd, perhaps recurrence in the small bowel).