One thing you can try is using a small magnet on the back of the device, or over the keyboard. As I recall the switch involved is magnetic. If you place it correctly on both track areas it may trigger it to think it's closed again? Worth a shot... And once it's back in normal mode, you can take backup-menu off so it will boot normally.

It would be nice to have a boot option for "reboot and ignore open slider for next X boots".