It's not Gehenna because it's only Gehenna when explicitly described as so. Death is not synonymous with Gehenna, it is with Hades and Sheol though.
When to apply Hades/Sheol vs Gehenna is subjective because the Bible only gives ambiguities when speaking of Gehenna.
BTW I am not a Christian, I am just playing the Devils Advocate here and using logic to reason out this topic.
-Sab