Keep or toss?

I just replaced a run flat tire under warranty worried that the sidewall was compromised from a pothole. I kept the old tire because when they took it off we saw the inner cords were perfectly intact and the sidewall became flush again. In the past I had tears through my sidewalls that developed into real bubbles but this time it only had an imprint from the wheel and the bulge was extremely minor. For now I'm keeping it as an emergency spare and the tire shop even said for emergencies I can keep it laying around. Without a load on it now the deformation is completely gone. What are your thoughts?