Leaving a nail in the sidewall of a tire is no big deal as long as the tire is not turning.
As soon as the tire starts turning then that is where all _ _ _ _ can break loose.
The air could come out all of a sudden and the driver could lose control of the vehicle and that would not be a good thing.
A tire shop will not repair a nail in a sidewall as that would be a big no-no.
About the only thing you can do is to replace the tire,,thats just the luck of the cards.