For me the annoying failure mode is when the metal ring on the puller which attaches to the slider eventually wears through and breaks (this seems to happen on bags and luggage a lot for me). The important parts of the zipper are all still working, it's infuriating that there isn't an easier way to replace the puller easily like for like (at least that I'm aware of).
Yes, paperclips are wonderful for this purpose, especially so when used on one's fly zipper as they've a low profile and can't be seen.
The best paperclips for this purpose are the V-shaped type that are narrower at the top. They've saved me from having to replace a zipper on a number of occasions.
If you read my comment about washing powders attacking the crappy alloy material that's so often used in those pull tabs and causing them to fail then a paperclip is the ideal solution.
