It is impossible to delete the original firmware. Rockbox doesn’t do it, and niether can you.
One of the nice things about Rockbox is that you can boot either to it or the original firmware at will.To boot into the original (Sansa) firmware when Rockbox is installed, press (& hold) the left (REW) button on the player while turning the unit on. It will boot into the Sansa firmware.
To then boot into Rockbox, turn the player off, then turn back on using only the power button.
