Interestingly, in the original script and filming, Duke was slated to die. But there was such a backlash from the Transformers: The Movie death of Optimus Prime, that at the last second, they changed the plot to have him pull through it.
And really last second too! That’s why you don’t see Duke at the end of the movie, you just hear Flint shout out in a crowd scene “Everybody, Doc just called. Duke’s gonna be A-Okay!” They had no footage of Duke pulling through.