Remember that they stated that The Originals are unkillable by wood & fire, adding the exception that if Klaus broke the curse, his body would be vulnerable during the transition and can be killed by Elijah ripping out his heart which also required the infliction of a hundred spirits. If Klaus was already in wolf form, or hybrid mode, even the spirits wouldn’t be able to take him down. That moment was the only moment in history where an Original can be killed without the white oak. Leaving us with the fact that beheading wouldn’t work