Repaired and now recalled Turbocharger has cracked the head gasket?

My car is seven years old and has 80k ish miles on it.  It's been dealer
maintained.  I don't use it to pull things.  I don't ride off road.  I drive about 15
to 20 miles a day and about half is on interstate and half is in the city.  I have
a great driving record, and car has never been wrecked.  In January, my car
was throwing some codes and running rough.  I took it to dealership.  They
said that it had a misfiring cylinder and the turbocharger needed replaced.  I
paid over $2,400.00 for repairs.  I had car 33 days and it overheated.  I
pulled car over immediately and had it towed to dealership.  They replaced
thermostat and put in a new battery.  Car drove 22 miles (I did not make it
home.) and overheated again.  I stopped immediately and had it towed back
to dealership.  That was on March 7.  I heard nothing from dealership.  I had
a loaner vehicle.  7 weeks went by.  I finally called and they said they had
fixed several things on car, but it still was overheating.  Meanwhile, GM
extended the warranty on turbocharger and reimbursed me for entire repair,
including cylinder coil pack.  Now, dealership tells me my head gasket is
cracked.  From everything I've read and the 200 engineers I work with - the
head gasket was cracked from the heat of the turbocharger the first time -
and dealership missed it.  In fact, the MAIN cause of a misfiring cylinder is a
cracked head gasket.  Furthermore, the entire engine is probably fried.  I
think GM owes me a new engine.  I have no confidence in this dealership's
ability to fix my car.  I think they know they missed it, since, they have now
had my car for 3 months.  At the very least, I think they owe me a new head
gasket and labor.  I have had a loaner car for them, but it is a huge hardship
for me. My husband doesn't drive much and we rely on the one vehicle.  I
just put braces on my kid's teeth and I just paid this car off 8 months ago.  I
anticipated NOT buying a car for another 4 to 5 years, while I saved my
payment money to pay cash for a new one.  WHAT should I do?