If endometriosis nearly infiltrating colon recurs after hysterectomy & does inflitrate, how do you know? Any kind of routine follow up typical?

Bloody stools. You'll likely see bloody stools or have cyclic pain like you did similar to when you had endometriosis before. Endometriosis is difficult to see with any imaging study, so there isn't a routine surveillance.
Depends. Significant involvement of the colon is usually with an endometrioma or fibroma, a benign growth in the bowel wall, sometimes seen on colonoscopy or at laparoscopy. If large enough it can be a cause of bleeding in stool or obstructive symptoms such as a major change in bowels. A colonoscopy will find a significant fibroma of the colon wall.
FOLLOW UP REVIEW. In cases of recurrent pain after hysterectomy, review of "uterus pathology report" can reveal whether diagnosis was appropriate. Concerned women can obtain report directly from hospital medical records department without need for doctor consent & then ask an interested doctor to review & explain. Private consultation with an interested doctor (i myself do for charity) is available at healthtap.