Good Day! Your catheter was placed to aid in the healing after your urethroplasty
procedure. So please maintain your catheter and call the clinic of your doctor to let him know what happened. If you're referring to the urine bag that is connected to the catheter, yes you may drain your catheter with a diaper while waiting for the opportunity to get a new urine bag.
I would like to say that the catheter that is not attached to a urine bag is more prone to infection and may affect the outcome of your surgery. Best of Luck.