For a pure hypothetical, if the checked bag gun was not detected. There are many ways people might approach this serious problem
After arrival at the destination, it would be unwise attempt to take the pistol back via an airline. A person could ditch the ammunition, rent a car, take the gun to Vermont, where you find a gun shop that will send it back to a gunshop in their home state.
They could attempt to change their flight to start in Pennsylvania, or another state with sane gun laws, and check the gun legally in that state on the way back to where they came from.
They could turn yourself into the police. This would likely result in prosecution.
They could field strip the firearm to parts, and ditch the parts in various places.
Just a few possibilities. I am not a lawyer, nor do I play one on TV.
You got it! Rent a car, drive safely to PA, go to a gun shop and have it shipped home. Take the hit on the Germany trip (and it’s becoming a shithole nation anyway).
Strip the gun into two parts and mail it home in two separate packages. Once you break it down it is no longer a firearm, it’s parts and not illegal to mail in the regular postal service.
You only need a dealer if the gun is functional. A frame without a cylinder, or a receiver without a barrel is parts. A pistol without a magazine IS still a gun, it is just considered unloaded. You could place a single round in the chamber and fire it.