the camshaft got hooked and thereby affected the valves and the timing chain needed replacement
What parts need to be replaced when the camshaft of this car gets bad. on 2009 Volkswagen Passat
Why did the camshaft go bad, it should not happen if the engine had frequent enough oil changes with the proper grade of oil. My fear would be that there would be other engine problems or bearing problems that may be around the corner. The mechanic working on the car needs to give you a proper assessment after he has done a proper inspection of things.
I agree with Pat. find the cause and the damage before proceeding with the repair.
I am not sure about the passat but there are a few recalls and bulletins on the camshaft wearing prematurely for the jetta. My Jetta is a 2007 and I believe the bulletin spanned a few years. Since yours is a 2009 may want to check into it.