At the first sign of trouble, he should have stopped, switched off the engine and called the garage. They would have had the option of collecting the car or of telling him to risk driving it back.
By failing to give them the option at that point, he has assumed responsibility for any subsequent damage caused by the overheating.
Just my personal opinion but I think that the garage will not be liable (or only partly liable) for the repair costs.
As to what he should do - speak very nicely to the garage and determine what went wrong and the options for repair. If he's calm and polite, the garage might just help.
At the first sign of trouble, he should have stopped, switched off the engine and called the garage. They would have had the option of collecting the car or of telling him to risk driving it back.
By failing to give them the option at that point, he has assumed responsibility for any subsequent damage caused by the overheating.
Just my personal opinion but I think that the garage will not be liable (or only partly liable) for the repair costs.
As to what he should do - speak very nicely to the garage and determine what went wrong and the options for repair. If he's calm and polite, the garage might just help.