How often does the rectus plication rupture?

It's unusual for plication to rupture. Plication may not hold up to the test of time producing more laxity but rupture is rare. 

Pictures would be helpful but it sounds as though your rectus was not plicated.  Let your plastic surgeon advise you of the best option.  

I think it would be very rare for the abdominal muscle plication to spontaneously rupture without a specific traumatic event that would stress the closure. Most of the time this closure is done with permanent sutures in multiple layers. Even with good muscle plication, however, not every abdomen is completely flat after abdominoplasty. This is most often due to fullness and fat that is located inside the abdomen which can not be addressed with the procedure. Even when this mild distention is evident, there is typically a significant improvement over the pre-surgery appearance. The muscle plication is part of every standard abdominoplasty (not a mini tummy tuck), so it is curious that your surgeon would have to refer to his records to see if this was done. You may have misunderstood him. Also, if the distention is very low in the pubic area, it can sometimes be a challenge to flatten with any abdominoplasty technique. I recommend that you further discuss the situation with your surgeon to make sure that he fully understands your concerns and that you understand what options are available. 

Unfortunately, after any surgery, there is a possibility that the patient (in this case, you) will be disappointed with the results. Thankfully this is not common and most patients end up very pleased. That fact, however, unfortunately does not help you. As my colleagues indicated, if your pre-operative findings suggested that you would have benefited from a muscle plication, which most women seeking abdominoplasty indeed do, then your disappointment with your outcome might be a reflection of either an incorrect preoperative assessment and treatment plan by your surgeon, or a suboptimal result from your surgery, or both. In order to determine how to best proceed, it would be wise to discuss your disappointment with your surgeon. If you are confident that he can revise your surgery to your satisfaction, then you should consider that option. Alternatively you can seek a second opinion for another board certified plastic surgeon qualified in aesthetic body contouring surgery, ideally a member of the American Society for Aesthetic Plastic Surgery (ASAPS). Best of luck to you. 

A rectus plication typically does not rupture. It is much more likely that you just did not have a plication procedure performed. Good luck