Putting diesel in a gas vehicle typically doesn't blow anything up. Doing the reverse (gas into a diesel) can in fact cause a big kaboom. But putting diesel in a gas system isn't an explosive situation. While it can absolutely wreck the fuel system including the fuel pump, the fuel filter, and the injectors, it won't go boom. In fact, it normally just requires you to drop the tank and rinse it several times with fresh gasoline. If it was actually run, the fuel system would certainly need some (expensive) replacement parts. But I have never seen a report of a gas motor "blowing up" from being fed diesel. Typically the diesel won't even get to the motor as it will just gum up the fuel system and starve the motor completely. I seriously doubt there was anything wrong with the original motor itself. However, given the OP's general lack of knowledge on this stuff, I strongly suspect a ripoff by the mechanic and/or shop making up damage that simply didn't exist. I'm curious - what evidence was given that the motor blew up? Was an itemized list of damaged components provided? Was any verification of that damage done? Did anybody see the parts that were replaced?