I’ve carried all my stuff in a belt pack since long before such things were fashionable and, quite some years ago, a friend made me a custom-sized one that’s been in constant use ever since. Of late, one of the zippers got cranky and finally failed completely.
An autopsy showed the middle of the cross bar on the tab had worn completely through, the stubs had bent outward, and the remains no longer engage the zipper tooth lock.
I replaced the tab with a short length of chain and a jump ring, but I fear the pack fabric is also reaching end of life.
The Smell of Molten Projects in the Morning 
You’re more sophisticated than I am…. I used a paper clip. Which reminds me I need to replace it as it’s starting to rust.
The jump ring was just so stylish… might even be stainless steel, although I’m not holding my breath over that.
I’ve made a number of replacement zipper tabs from a short run of tubular chainmail using stainless steel rings. They’re very comfortable, but generally by that point the item in question is at its end of life, like yours.