I have had my 02 about 3 months now and it just turned 100 k. My mechanic said as part of the 100 k service it should have a new timing belt and all that goes with that. He also said that when one breaks the engine is trashed. Is this true?

yes if it breaks your looking at a new engine . you need to change the water pump and at least the bypass hose if not all of them. the water pump and bypass hose are deep in side the engine but a walk in the park at the time the timing belt is done. the other hose could be change with out removing a lot of parts also all 3 small belts must come off so why not put new ones on in stead of the old ones.