Ah, now that's an interesting question. I do think that the phenomenon of people photographing QR codes in order to avoid typing in URLs has peaked, although I say that on the basis of industry gestalt rather than Google logs. But hey, it's a barcode. They don't die. We'll continue to see them around, even if it's just in situations where other barcodes would do just as well, like on boarding passes.
My original response was ill-phrased, since it implied that Google might decide to remove QR code generation from within Google Image Charts. That will not happen. What might happen is that Google could turn off all of Google Image Charts.
If that happens, I think you won't have too much trouble finding an alternative solution. Chart generation can be difficult to do well, but QR code generation is dead simple.
Jon