The article says a few (if I remember correctly) will be refurbished, so that means the majority will no longer be counted as usable. So again my question, what happens with them if not being disposed?
According to the article you posted, the Stingers were scheduled to be refurbished, not disposed of. So, again the answer to your question is that if they aren't disposed of, they are refurbished.
I wonder what the cost difference is between refurbishing a Stinger and manufacturing a new one.
I'm not military, but I do deal a lot with inventory and supply chains. It seems like some posters are doing a lot of mental gymnastics in order to reach the conclusion that weapons supplied to Ukraine by the US somehow "didn't cost the US anything" or "were going to be thrown in the trash". On its face both claims seem dubious.
We have inventories precisely so that we have items when we need them, and don't have to spend literally years ramping up production -it's as simple as that. It's not some mistake that we maintain armories filled with everything from Javelin missiles to Humvees, it's by design. We also have relief valves built in to control the supply. A major one - training - was pointed out by
@Michael in ABQ. We
want our troops to get live-fire training but we don't to manufacture new ammo just to have some junior enlistee shoot it into the sand halfway to the target. But there's another head-smackingly obvious reason we stockpile munitions, and that is
to supply nations like Ukraine (or - more accurately - countries we think are in our best interest to arm. Sometimes we provide weapons as "aid" and in Ukraine at least it seems to have had a phenomenal ROI so far. In many other cases we sell these 'outdated' and 'near end of service' caches to other countries, earning quite a bit of money in the process . And of course we always keep a crap-ton at hand just in case they are needed for domestic defense. When these missiles were being produced some 30 years ago we didn't have a clue what they would ultimately be used for, but the brass was quite certain that they could be used for something, at some point, somewhere, and they were right.
And of course there's the whole "industrial-military complex" - making and sending out munitions is an enormous jobs program here in the US, with >$150B spent annually for 'private' companies to build bombs and bombers, employing a civilian workforce of almost 1MM people.
Authors note: I'm in no way endorsing the US's model of supplying half the military weapons in the world, but merely pointing out the flaws in saying these misses were headed to the landfill if only Russia hadn't invaded Ukraine.