There are some people around that don't believe that can happen to a usbkey, but since I have lost about 3 that way I know differently. All three had to be thrown away as they were completely unusable. In my case though one was due to a crash with the drive plugged in but the other two were due to me forgetting to unmount them before removal. This is the reason I hate usb automount so much. My theory (and it has worked for me so far) is that if you have to go to the trouble of mounting a device then you will probably remember to unmount it too. If it has been mounted automatically you might not. Probably the easiest way to not forget to unmount something is to have an icon either in the tray or on the desktop when it is mounted (and not mixed in with dozens of others so it stands out). The makers of desktop environments could help enormously here but seem to be unwilling to do so. The KDE3 storage media applet was the best example of how it should be done and the KDE4 removable devices applet is the worst example (because it looks exactly the same whether or not anything is mounted). Gnome's default setup is about as bad as KDE4 you either get icons for everything or nothing both of which are useless. (there is a way around it though).
The Alt/SysRq route would have been the only way to save your disk though. There are some distros where the Alt/SysRq function is not enabled by default, I don't think Mint is one but I am not sure, so make sure it works before you actually need it again.
Fujitsu Lifebook AH532. Intel i5 processor, 6Gb ram, Intel HD3000 graphics, Intel Audio/wifi. Realtek RTL8111/8168B Ethernet.Lubuntu 13.10,Ubuntu12.10 (Unity), Mint16 (Cinnamon), Manjaro (Xfce).