The muscle plication (erroneously termed a "repair") in a tummy tuck relies on two main factors for success - 1. The sutures must hold the plication, 2. The patient must comply with garments, lifting/activity restrictions.
It is unusual for the sutures to "fail" from a plication. However, a bulge can occur if the knot breaks or the sutures tear through the fascia. More commonly, patients return to activities sooner than advised and prior to the scar being strong enough to resist the activity. I restrict activities which stress the plication for 3 months post surgery and keep all of my abdominoplasties in compression for a minimum of 6 weeks. Although no postoperative routine is a guarantee, these limitations have made bulges a rare occurrence in my practice. As for who pays for a revision, that depends upon the office's revision policy.