I love the concept of a shattered glass au where the cons do in fact lose and Megatron is forced to join the LL crew. I mean I know it would never happen but primus do I love the concept of sg Megatron if the Decepticon's lose going on the very same journey his cannon counterpart when on but in the opposite direction. Let him slowly fall to the Autobot's side the more he's with them, originally doing so to make an easier escape but in the end does actually get close to a few cough cough Minimus and fall for Rodimus genuinely (yes megarod shall appear, I must be faithful to my otp) and just become one of them. Let Drift be an instigator for it as he was once a con, one of Megatron's most trusted.
As said I know this would be a hard concept to play with, sg Megatron wouldn't just switch sides but... I do love the concept of him doing so. So it would have to be oh so slow, like... the slowest fall that has built up and development behind it. Of course I could go the simple route and have Rodimus join a con crew where Megatron is the captain and have him go on the same journey as IDW Megatron did and become good blah blah blah...But where's the fun in that? Imagine the internal self hate and guilt Megatron would have over disbanding his cause (even if he was forced to do so he'd hate himself for it) and not only being forced to join the enemy but genuinely falling for an Autobot? cough cough Rodimus would be amazing for a fic.
(Now this concept could also be applied to sg megamags/minimegs, but that's a blab for another time)