I have a question to ask ,what if Ultra Magnus manage to open the matrix and become Magnus Prime during attack by Galvatron in the planet of Junkion in G1 ? Can Unicorn still can be defeated since all the power already used in the Matrix ? Do you think Optimus Prime already know Hot Rod is the chosen one of the matrix to destory Unicron one day however he pass the Matrix to Ultra Magnus is just a plan to fool Unicron and Ultra Magnus don't know that plan ,only Optimus himself,Ultra just a spacegoat ? Thanks.

if things did not flow as they did and the matrix were not taken to unicron by galvatron there is a significant chance the timing might not have aligned for unicron to be defeated and cybertron would have been destroyed

If the Matrix opened there, Then Galvatron wouldn't have been insubordinate to Unicron And he would've sparred his wretched planet of Cybertron.

There are lots of ways to defeat a Unicorn. Cosmos would have stepped up and killed Unicron sans matrix. Again.

Ultra Primagnus is what would have happened! I love Hot Rod, but I thought the previous holder of the Matrix chose his successor. So yeah, Hot Rod was meant to rise from the ranks and light their darkest hour... but afterward, give the matrix back to the person I chose to lead the Autobots, and not require me to have to return as a zombie, be destroyed by my own bots, then resurrected again to lead the Autobots because you were never meant to be a Prime. Really kid... a Winnebago? Ultra Primagnus FTW.

Unicron would still be around.Maybe planet Junkion is the one destroyed. Or Junkion suddenly breath his own life,a primus-wannabe.oh wait,that's the allspark's doing

I get the distinct impression the Autobots would have had a leader that wasn't responsible for the death of Optimus Prime. Of course in the current canon (IDW comics) Hot Rod is somewhat...incapacitated, at the moment