Is There Chances Of Renal Failure Post Urethral Obstruction Surgery Of Kidney?

HELLO! I HAVE A FRIEND WITH ONLY ONE KIDNEY RIGHT NOW. ONE OF HER KIDNEY WAS REMOVED DUE TO HYDRONEPHROSIS AND NOW HER OTHER KIDNEY HAS A URETHRAL OBSTRUCTION WHICH WILL BE FIXED BY SURGERY SOON. SHE IS 27 YEARS OLD AND HEALTHY OTHERWISE. I WOULD LIKE TO KNOW HOW MUCH COULD THIS SITUATION AFFECT HER LIFE FURTHER. WHAT COMPLICATIONS CAN OCCUR? DO YOU THINK SHE HAS A HIGH CHANCE OF RENAL FAILURE?