Car jerks

Actually on way home Fri, check engine lite came on, temp shot past "H" & car shut down -- overheated I suppose, had towed, was told this AM, I had a hole in the radiator that caused the coolant to mix w/the transmission, all the fluids were 'mixed'. They're replacing the Radiator, said this is a definite to get the car runnign again, replacing trans filter & doing a coolant flush & transmission flush & seeing IF this was the problem & corrects it, this is 'Best case scenario' I was told - worse case is all the 'fluids' could have gotten into the transmission/engine, (think he mentioned a head gasket!) & I could need a whole new transmission/engine - What are the chances I'm facing a 'worst case' scenario & having to replace a trans/engine!