Durability protects against item destruction by enemies. Enemies cannot equip an item before the current equipment part is destroyed (or the slot is empty). Of course, enemies also don't destroy equipment from their "region set", so the prisoner set for the Ratkin. So it would have the effect of making the item harder to destroy (and potentially replace) in other regions. But yeah, higher durability would make sense.
I like the concept of the item having a chance of destroying items, or equipping other ones. Although I'll need to do some testing whether it's balanced. It's certainly possible to implement. And damage reduction is always a safe, albeit boring, thing to put on cursed equipment.
Currently there's no mechanic for removing cursed equipment early, since the curse (in this case, reach level 3 of prisoner) applies immediately. But it might be a fun mechanic, where you have to hope the curse doesn't set in before you can uncurse the equipment at the guild.