it shouldnt really happen to a car with a decent service history, ive never heard of an engine having to be replaced due to a broken camshaft, are u sure they werent talking about the crankshaft? some cars when the timing belt breaks snap the camshaft(older ford 1.8 diesel engine for example) but can still be repaired fairly easily without having to resort to replacing the engine. unless the problem occured due to a common fault with that particular engine ie the camshaft being starved of oil or something to thta effect, keep chasing vauxhall for an explanation