Hey, the HDMI not enabled-error is not the reason for the fstab-mounting-and-not-booting. It is shown whenever the boot process can not finish (I think).
You have to tell fstab to mount the disk only if present and without waiting for it at boot. The option is called nofail (there is also nobootwait, but thats not supported)
You have to add this options in your fstab-line:
UUID=XYZ MOUNTPOINT FILESYSTEM defaults,errors=remount-ro,nofail 0 2