Either have a movie or flashbacks set before AoE. What got me thinking is that Lockdown states "Autobots and Decepticons making a mess of the universe and I have to be the one to clean up your mess". What's to say that he hasn't visited other planets and killed Autobots or Decepticons?
All I'm saying is if people wanted him back that's a say to do it, not that they should bring him back.
How about the AOE Lockdown was merely a drone and The creator have an army of him cleaning the universe for them
Lockdown is done. We haven't seen the Fallen since TF2 and Sentinel Prime didn't appear at all in TF4
I loved Lockdown but I think it's best to keep him Dead. If was to appear again he should have been left alive.