@wmd Quick-ish fun fix / less complex is:

1. Get another zip (donor bag or drawer somewhere - find or wait for another bag zip)

2. Cut out this zip,
(straight cut or not new will cover the repair)

3. Sew the new to edges of old (literally the most basic sew, lots of times = strong zip)

Colour-matching thread
(unless you want to show off your repair as it actually looks cool as "I re-used this" rather than perfect China/Tahailand/Waiwan looking new bag) :)

What do you think - maybe the size is a bit non-standard but even that you can cut to size I think!