2003 Lexus GS 300

Engine Cooling problem
2003 Lexus GS 300 6 cyl Front Wheel Drive Automatic 97000 miles

I took my car for routine maintenance to have the timing belt and water pump replaced. The next morning while driving I smelled a burning smell and the check engine light came on. As I was trying to get off the interstate the car went dead. I am now being told that a hose " came loose" allowing the coolant to leak out. The mechanic is assuming full responsibility and is repairing. He mentioned having to replace the gasket. My question is, should I be concerned that serious damage was done to the engine? If yes, how will I know?
September 30, 2010.

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