What's the problem preventing extraction of the bolt? Is it broken off (below or above the deck?), rounded head, just plain stuck, ... ? These are rather substantial bolts, in a good oldfashioned iron block, so he should be able to get it out.

Of course, considering the work that might be involved, especially if it's broken off deep below the deck, your mechanic might think it more cost effective to just replace the engine. How many miles are on it and what is its overall condition? Pulling these engines isn't all that much work, and if it means saving the purchase of a replacement head, gasket set, etc....

Bram