I had a very odd idea after viewing Beast Machines for the third time (I'm a much bigger fan of Beast Wars than I am of Beast Machines
).
I imagined what would happen if Megatron had succeeded, merging himself with the Matrix and consuming all of the Transformers' sparks into himself to become a supreme being.
I imagined that he could have actually become the being that we know as Unicron. He turns Cybertron into his new body (the monster planet we're all too familiar with from the '86 movie) and uses Transwarp technology to travel back in time, intending to consume the Matrix itself and prevent the destruction of himself (since he read in the historical archives that the Matrix was used by the Autobots to destroy Unicron).
In doing so, much like what happened in Beast Wars, instead of accomplishing his goals, he simply fulfills what history had written. In attempting to destroy the Matrix of leadership and prevent his own demise, he fulfills it and is destroyed in the past.
The end result would be a time loop of sorts, where all life on Cybertron ends with the singular event of Unicron's (BW Megatron's) transcendence into godhood, where he travels back in time to prevent his own demise, only to meet his doom.
Of course, this concept flies in the face of several origin stories to Unicron (not to mention the entire existence of anyone called 'Primus'), but it was just a thought I had.