I ran into this the other day when I deleted a filesystem and tried to reboot. The system hangs. The easy way to overcome this is to connect in single-user mode and edit your /etc/fstab file. Well, you can’t do that unless / is open rw. Use the following command to reopen / in rw so that you can edit /etc/fstab.
mount -n -o remount, rw /
Once you have edited /etc/fstab you can reboot and let the system come up normally, then fix your drives.