I would really let the dealer have it on this one. Something as basic as this and they can't get it right. I would be a little hesitant to go back as you never know what "little insignificant" work they will skip out on next.
And I would say that odds are there was no damage done to the engine. Its not the best for it but engines are pretty tough. I wouldn't delay any planned mods just because of this either.
