This website promotes the Good Sam towing assistance insurance. I sure would at least consider getting it. Let it break in is an incredibly sarcastic dump on common sense. If the shop is ATRA automatic transmission rebuilders association member you are covered at any other ATRA shop. If not pleasantly explain to your shop management that if the transmission breaks your next trip it means pursuing a criminal charge of fraud with your local District Attorney.
As a note - factory remanufactured transmissions are light years better than most independent reman units.
Uh gee your rebuilt engine has a connecting rod sticking out of the side of the engine block...
Oh, give it time, it'll get sucked back in...