I have just come up with an even bleaker alternate ending for The Transformers the Movie.

Instead of gloating, Megatron shoots Optimus dead, and with the other Autobots plus Daniel stunned, Megatron orders the Decepticons to finish them off. Once they are dead, Starscream shoots Megatron from behind and kills him off, claiming leadership. But the Decepticons are not easily swayed and they kill him, now they're left arguing and fighting as to who should be leader.

In the end, all of the Decepticons die killing each other.