Simple he doesn't. She marries someone else.

Yeah, but don't forget the real reason he leaped in here was to give Buddy Holly the lyrics to "Peggy Sue". He had been playing with "Piggy soo-ee" and it wasn't working...

And the only reason he was singing that was because Sam said those words while he was looking for Piggy, who he named.

It's odd... my interpretation of the pilot episode is that Sam's first leap (in which he told people he wasn't himself) began a chain reaction that disrupted time and he now has to correct them. Except had Sam never leaped, Buddy Holly would never have thought of Piggy Sweet.

Given that How The Tess Was Won is set a little over a month before Genesis, it seems unlikely that the problem here could be a consequence of Sam's first leap.

Why would you say that? If Sam changes the timeline, it would be instantaneous.