Steps to restore the original firmware:
* find the clppa.bin file (this is the original firmware file), you can find it in a .zip on the sandisk forums
* boot the clip+ in the original firmware mode (hold the LEFT button while booting it up)
* verify that the clip+ has > 50% battery left
* copy the clppa.bin file to the clip+
* safe-remove and unplug
-> clip+ should update its firmware now with the file you just copied, thereby removing the rockbox bootloader
* once the rockbox bootloader is removed, you can remove the .rockbox directory