It's their problem, not yours. Even if the post office is closed after they're done working I don't see why they can't switch to like UPS or FedEx and schedule a pickup. The cost will probably eat the profit but it's their responsibility and if freight is going to be such an issue they need to charge enough that they can get a freight option that works with their lifestyle.

Like Magedragonfire said the dispute window is much larger than it used to be.