This emissions stuff is getting so out of hand. Near as I can figure there is 7 counties that require an emissions inspection in Ohio and since he has not found out that the cat was missing until now, chances are you are not in one of those counties. So, the "I didn't know, you bought the truck", go pound salt would be fine. There a dealership for crying out load at $1000 dollars a pop, you would think they would look for that. I wouldn't loose sleep over this.
FYI, you can core out a CAT and for $8 dollars fake out the engine ECM to think the CAT is still there and in most states there emissions inspection won't find it.