It's really difficult for me to understand how this problem came about. The vehicle went is for a radiator replacement, and now the PCM is not working? All I can say is that I have removed, rebuilt, and reinstalled many Jeep engines, radiators, and transmissions in my time, and never once have I either destroyed a PCM or any control module in the process, or found that some control module "just stopped working" after a repair.
It just does not seem right or possible for the mechanic to claim that the PCM is now faulty after a simple radiator replacement, unless he purposely destroyed it, so if I were in the OP's position, I would sue the shit out of both the mechanic, and if he works for someone, his employer as well.