The one thing I could foresee depleting my ample stock of .22 RF would be bartering.
1) .22 RF is the one ammo type that I have more than I would ever shoot. Especially the bulk ammo. So this is ammo that I would not feel bad about trading for something I need.
2) .22 RF is much less of a threat to me and others than centerfire ammo.
3) .22 RF would be in demand, now and in the future. It is very common and most people would have a .22 RF firearm that they could use the ammo in.
4) .22 RF is less expensive, so even at inflated prices, it would serve as a small denomination barter item.
I don't think a person could have too much .22 RF ammo - there will always be some use for it. I will always be buying more, but I have shifted my buying from bulk to precision hunting ammo.
As for it no longer being made - it would have to be a SHTF situation. Maybe, in 100 years or so, man portable rail guns or even energy weapons will replace firearms, but .22 RF and air guns will be the last to go. I am thinking that rail guns/energy weapons would never be something that any government would let civilians have.