Zip is always on - so you can fix it
So far I've always thrown away such zippers that opened in the middle of the spiral as "broken".
On the occasion of dealing with the threading of a zipper, I have withdrawn in such a broken zipper zipper completely from the spiral, so had the tape ends separately in the hand and threaded the zipper again.
See there: Although the zipper was about 1.5 cm shorter than before, but could be easily and permanently close again and did not burst on!
