Awesome.
I got a better alternate timeline.
Suppose Grievous killed Obi Wan, and then proceded to another Sep controlled planet when order 66 came around? Surely, the kaleesh woulda' figured out what was going on, then proceded to kick Anakin's punk ass around on Mustafar (killing him outright instead of leaving him for the flames), and led an ongoing war against the "Empire" as it was being reorganized. Plus, with no news of Grievous's death to report, Windu would have stayed in the temple, an reported the news of the identity of Sidious to the other Jedi masters, giving them a pretty good warning not to trust the clones. One more master at the temple would have definitly put a dent in the 501st. I'm not sure if there were any jedi masters in the temple at the time...

...

I think you're all missing a key objective here...

If Greivous' command cruiser had gone down, taking along Anakin, Obi-Wan and, Palpatine (assuming that Anakin has already killed Dooku) then it would effectivly have put an end to the Sith. The "true" Sith would both be dead leaving only Dark Jedi to rise up and fill the void (not that this hasn't happened at least a dozen times in the history of Star Wars EU).

The Republic would have continued its slow decay but without a strong, charismatic central figure (such as Sidious) to bring everyone together I think the Jedi would have easily 'cleaned up' the senate.

Precisley. But, assuming the cruiser didn't slam into the palace, Amidala would still probably give birth to Luke and Leia, assuming she didn't leap from the palace upon hearing that Anakin had been killed. If and when the Jedi learn of how she got her children, etc, would they have trained them to be Jedi???

Not if Windu and the other cockmunch Council Members were still alive.

They didn't want Anakin trained in the first place and, I'd imagine, despite their "enlightened" sense of morality, that the Council would refuse her children training even if they were 'uncovered' at a very early age. I have very little respect for the Council created and portrayed in the first three films (I much prefer the Council of the EU and whatnot far more).

That being the case Amidala may look to outside sources to train her young ones; further exposing them to the corrupt sort of Force-User that exists beyond the Jedi.

Luke and the other one (heh) would then grow up to be cruel Warlords who would crush the Republic and remake the Galaxy in their own image.

Vader would never have existed and as such the children would live in less of a shadow.

I think your right about most things, except they wouldn't be necessarily dark sided about the whole affair, rather I would suspect that they would create a New Jedi Order while the Old Jedi Order denounced them, branded them as evil, and tried to eradicate them. Another Civil War would erupt, and in the end, Luke and Leia would be ruling the Republic, re-naming it the New Republic to replace the Old Republic and the Old Council, and would put the surviving Senate Members, say Mon Mothma, etc., into power.

Well, Otaku, you're wrong.

Dead wrong.

If Grevious had won instead, Grevious STILL serves Palpatine. And do you want to know what Palpatine would do? He'd let his 'Palpatine' persona 'die', and Grevious would announce the revealing of his commander whom the CIS had kept hidden as to keep safe and instead it would be Emperor Sidious we'd be writing about instead.

You see, Palapatine covered all his bases and for many eventualities. One way or another, he'd end up as the leader of the Galaxy.

i have to agree with that.

the chess master of starwars award goes to Palpatine.

Oh but I agree with Beff. The Jedi Council of the Old Republic were stuck up and corrupt pricks just as the Old Republic was and would fall apart eventually.

As for Luke and Leia becoming Warlords? The problem they had with letting Anakin getting trainning was that he was what? Twelve? They had their reasons and would right out deny anyone. If not for Anakin's strength in the force he'd have been denied to.

So, like... in the end everything more-or-less turns out the same.

Heh.

So, to answer the first question...

What would happen? Everything would still play out to a similar ending.