In this case I'm thinking of the time just a few months ago when a hose clamp that was misplaced during a cooling system overhaul caused a head-gasket-damaging overheat... which cost $4800 to fix.
Now what if the shop said, in your example, "too bad, we're not fixing the head gasket"? I'll start with saying that court is probably your next option. But I have two other things to add. First, a decent shop would replace the head gasket if they screwed up. Once in a while a shop just has to eat a big job due to a screw up.
Second, though, is that it's sometimes hard to properly place blame. I don't know the details of your situation, so forgive me for assumptions, but head gaskets don't just blow the instant the overheat light comes on. Yeah, the shop may have screwed up, but that doesn't absolve the driver from pulling over when the light comes on. So who do we blame? Well, that's why you call a lawyer. :)