You learned a vary valuable lesson don’t attempt to do an “apt-get” to update the My Cloud firmware. Not the first time someone has done it and asked how to recover. If you still have SSH access you could try an firmware update to see if it restores the content you deleted, provided portions of the firmware are still there. Note make sure to use the latest firmware version for your My Cloud. The directions below are for the v4.x firmware My Clouds.
https://community.wd.com/t/how-to-firmware-update-via-ssh/95476/2
