thats a big i'unno. depends on the chips, the controllers, the usage of the drive, etc.
personally, usb sticks are basically a commodity consumable (especially if you get them at the sweetheart size) and i don't consider it wasteful to replace them after 3-5 years if you are doing anything remotely important with them.
but if you just have them for transfering files from one PC to another in your own house, where a loss won't be catastrophic, just a mild perturberance, then use it till it physically doesnt work anymore