From memory I've counted at least 4 Zetec timing belts I've done where there's been a failure. One of them the tensioner had fallen apart and was running lumpy but re timed with a new belt saved it. One a water pump seized and shredded some teeth off a belt and that ran again with new pump and belt etc. But from experience 100% of all the Zetec heads I've done when a belt snaps while driving its trashed the valves. Sometimes u can be lucky