Its going to do damage, weather on tickover or moving, more so if it goes while on the move, and yes it can cause major damage. Not sure how to change this particular one, bit it uses the same engine as the fiesta diesel and I did mine in about an hour and a half when I had it. If your handy with the spanners I'd deffo give it a go. If not, best leave it to a garage, also get the water pump changed at the same time as if this goes, its a complete strip down again.
thanks mike for your reply,was the engine the same 1.4tdci in your fiesta & did you need the locking kit to do it ?will change the water pump if i do it as its sods law that if i dont change it that it will fail a week after !