Twice in a Lifetime - Season 2 Episode 22 The Choice

Ryan gets a second chance to return to his teenage years to prevent his father, a successful doctor, from having a heart operation which led to him being brain damaged. He always blamed himself as he had talked his father into having the proceedure. Mr. Smith gets to spend time with them and Rachel, Ryan's sister, lets him know who she thinks he really is: their guardian angel. Despite Ryan's pleading, his father still goes ahead with the surgery, this time with no complications and Ryan's finds himself not as a doctor - but as a priest, which he had always wanted to be.