system
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human
[Star Wars] Against all odds, Maul does the impossible, defeating and killing Darth Sidious on Mandalore. How does the rest of the war play out?

After Sidious kills Savage, Maul attacks the Emperor with renewed ferocity. His former master quickly takes the upper hand, until Maul feels a moment of extreme clarity with the Force, spotting a miniscule opening in Sidious's defense and landing a clean, fatal blow with the Darksaber. Sidious's eyes widen in disbelief at the hidden potential in his former apprentice, but he dies before any last words can be exchanged. Maul is now the true Dark Lord of the Sith.

How does the rest of the war play out? Does he consolidate his rule over Mandalore? How does he deal with the Repulic invasion? How does he deal with Count Dooku?
gpt
Short term:  

Maul consolidates his rule over Death Watch, who consolidate their rule over Mandalore. Under their leadership they reject Republic interference; the Republic begrudgingly agree to respect their wishes as the change in regime was a result of "local politics" and none of their business. 

As de facto ruler of Mandalore Maul leaves the day to day shit up to Death Watch, he has other things to worry about. Like Dooku. With Sidious out of the picture, he's also vying for the position of being the *true* Sith Master. Needing to both eliminate the competition and find a new apprentice, Maul kills two birds with one stone by courting the only dark side user powerful enough to challenge Dooku that also has a major vendetta against him: Ventress.

Ventress however is done with the Sith bullshit; Maul recruits her on the premise of revenge on Dooku for the deaths of the Nightsisters, with the plan of convincing her into becoming his apprentice down the line. Ventress agrees to take up her vendetta once again because she sees that Maul is powerful enough to challenge Dooku, after all he killed Dooku's master. He eventually wins her over by giving restoring her sense of belonging not only in the Master/Apprentice relationship, but as fellow Dathomirians. 

After extensive preparation and training, the pair, aided by Death Watch, eventually assault Dooku's forces: Death Watch takes on Grievous and his forces, while Maul and Ventress go for Dooku. 

The Sith pair win, but at great cost: Death Watch manage to repel and critically wound Grievous, forcing a retreat, but are wiped out in the process. Dooku is killed, but not before critically wounding the pair: Maul loses his arms and his robot legs get destroyed, Ventress loses a hand. 

The two retreat and recover. Maul gets new robot arms and legs, Ventress gets a robot hand. One day Ventress slips away: With Dooku dead and the Night Sisters avenged, she realizes she doesn't have the same ambitions for power as Maul does. Maul is pissed when he finds out.