Q: Got a flat tire had to get it plugged. Tires are under warranty but dealership said it has to be leaking

Yes, this is a sound repair. I don’t call any repair permanent as a matter of principle. If the repair was done appropriately, it will last the life of the tire. The dealership would make the same repair. If that repair fails, it is the responsibility of the person who did the repair to make it right. If you were out of town and could not make it to the dealership, the best thing to do is contact the dealership to see how it should be handled before the repair is done. The details of how it is to be repaired in such a situation is dependent on the warranty contract.

This is all assuming you have road hazard warranty through the dealer. Some tire damage is not repairable. At which time the tire would be replaced. Most of the time, a tire is repairable. If it is holding air and not leaking at all, then it was repairable. Most tire shops are well versed on what is and is not repairable.