In reply to jimtitt:
Depending on how it is made ( and assuming the zip itself is fine) you can sometimes prize off a stopper clasp thingimy and remove the slider and replace it with one ( of the same size/type) that is not worn.
( assuming that the pliers trick goes not work at least for a while. )
Less hassle ( just) than unpicking all the stitching and replacing the whole zip.
Post edited at 17:47