There could be some damage to the head hard to say with out removing the head. As far as lower engine damage it is possible with no plug because you have no fire in that cylinder so it could have washed down the cylinder walls and cause scoring. Anything like a pebble ect... could have went in the hole would have caused damage to the piston.Make sure the threads are not damaged where the plug goes or it will blow the plug out of that hole if you put a new one in. A simple compression test can be performed to determine and damage and a cylinder leak down test should be performed to assure the valves are not damaged.
I hope this give you an idea and I would make sure that shop makes it right for you.Thanks for the question
