Maybe when something comes along to replace "save"?
With the steadily increasing amount of software that auto-saves without you noticing, maybe soon we just wont need to "save" anything. It'll just happen.
My guess is never. The universal train icon for signs has a funnel and a cow-catcher, and it's a long time since a train looked anything like that.
Same goes for the universal sign for telephone - nothing like a modern cordless handset.
We can already seen this in action as the icon for 'mp3' on signs looks like a first-gen ipod. Already no players (even ipods) look like that, but I think it will stick around for a long time.
Some things get stuck as icons and the original meaning is lost with the sands of time. Once the icon is assigned to a meaning for most people, it sticks. There's no reason to update the icon, even if it no longer represents the object, because everyone agrees on the meaning.
There's only a handful of apps on iOS that include a save button, and even of those that do include one, DocsToGo is the only one I can think of that uses a floppy for a save icon. It might be gone before you know it ... though I'd guess you'll still see it in Windows in 2020 or beyond ;)
