Diastasis recti sutures coming undone? Can the sutures come undone years later, leaving me with a bulging belly again?

If your tummy was flat after surgery and remained so for some time, then it is very unlikely that a recurrent belly bulge years later is due to the diastasis repair sutures coming undone.  Initially, during the healing phase, the muscle plication sutures are critical in holding the rectus muscle together.  However, the resulting scar tissue is what ultimately holds everything in place and provides strength.  It is possible for the muscle itself to relax and stretch over time if the muscles are weak -- age, weight gain, disuse, previous surgery, subsequent surgery, large-volume meals, etc. are some of the factors that may have a significant impact on later development of abdominal bulging. Of course, an abdominal hernia must also always be considered if there is bulging.
In the absence of a hernia, weight loss (if there is excess intra-abdominal fat) and abdominal exercises may correct the bulging.  If your abdomen does not respond, you may well need a redo tummy tuck with additional muscle plication to restore a flatter tummy.  

Thank you for your question. After several years it is unlikely sutures hold your muscle anymore. It may be hernia or laxity again other. Please see a PS for evaluation.