A 3.5" floppy is the standard icon for "save". The same way that your cellphone probably shows an icon of a (paper) letter when you get a text message, even though no paper was actually used in transmitting the message. The floppy disk icon will survive its tangible incarnation, although nobody uses floppy disks to store data anymore, and hasn't for some time. In fact, the floppy disk itself hasn't been floppy for some years. Don't change a widely understood icon for no good reason, you'll likely confuse your users (notwithstanding the fact that the floppy icon is perfectly recognizable in low resolutions as well, something that's not easy to achieve with a pendrive).