Brake Masters They fried my engine! Tucson Arizona

First, I don't work for them so don't even bother saying such a thing because you don't like what I say.

The warranty would only cover the work they performed.  You clearly had an overheating problem.  They installed the "stop leak" in case there was a radiator leak.  Apparently the overheating problem was either caused all along by the head gasket leaking which they DID NOT repair...or...the stop leak did not solve the problem because a radiator leak was too large to repair by such "jury rigged" repairs, the coolant leaked out and you ran the car hot until the head gasket blew. 

In this instance, the repair was not sufficient as opposed to "faulty".  In court, the term "faulty repair" is different from "insufficient repair".  As such, there would be no "malpractice here".  If they advised you the radiator was bad and they gave you a choice of the proper repair of a new radiator and the cheap "repair" (maybe) of a jury rigged substitute of "stop leak" then it was your choice to go the cheap route which does not always work.