What if Padme and Anakin never got married?
Would the Galactic Empire still have been formed and Anakin Skywalker still becoming Darth Vader? The question is not a "could", which expresses a possibility either way, its a "would", a definite yes or no question!
I say no!
If Padme was never pregnant, Anakin possibly never would have been driven to the darkside by desperation. He would have stayed on the lightside.
Yoda and Kenobi were Order 66 survivors, and both were exceptionally strong, which was what helped them survive Order 66. With being such a powerful Force User such as Anakin being on the Jedi's side, he most certainly could/would have survived Order 66 alongside his fellow Jedi compains yoda and kenobi.
And a young (without the suit) Anakin could have most certainly killed Sidious in a fight.
If Anakin in ROTJ, killed Sidious as a middle aged man stuck within a robot suit, with less than half of his potential force power, then a young and agile anakin without the suit could have done that. On Youtube, they show some ROTS video games where Anakin kills Sidious in the Chancellor's office, as early as ROTS, young, agile, and without the suit.
While I believe that without Anakin being found by Qui Gon, the Galactic Empire still would have been definitley formed anyways, in the other hypothethical situation, that Anakin still becomes a Jedi but doesn't meet Padme, it's quite possible that the Empire/him becoming Vader never would have happened.
Now, without Padme's pregnancy (sidious's plan never could have been dependent on something such as that), Sidious had some backup plans such as poisoning her with Sith alchemy or making Anakin think her political enemies would kill her, so Anakin would turn to the darkside to save her, (a millenia old plan obviously had some back ups, there were other ways to put Padme in danger!)
However, if Anakin never met Padme, Sidious would never use her life being in danger to lure Anakin towards the darkside, and thus Anakin stays light and kills Sidious in ROTS, after order 66 presumably, preventing the Empier and it's atrocities, such as the death star blowing up alderaan, from ever happening.
To quote Lucasboy himself!
"Their love is complicated - pure yet forbidden, personal but with profound ramifications for an entire galaxy. Somehow, John has managed to convey all of that complexity in a simple, hauntingly beautiful theme."
Their love has profound ramifications for the entire galaxy, which goes along with my theory.