Assuming that Maul's attack on Qui-Gon and Obi-Wan was successful, what were Sidious's plans for Maul?
I find it hard to believe that Maul could have acted like Tyranus, i.e. the figurehead of the Confederacy, because Maul is so demonic. I don't think he would have had the political support that Dooku did (even though he did form an alliance of criminal syndicates, this is different as he 'spoke' their language of fear and violence).
I'd prefer Disney canon, but legends is fine too.
Sith Lords didn't always take apprentices that they expected to last over the long haul. They were simply a tool to help them achieve their goals and were frequently cast aside in favor of their own self-interests or in favor of a younger, more powerful replacement.
This is perhaps illustrated best in Return of the Jedi with Palpatine's willingness to cast aside decades of service from Darth Vader to replace him with Luke:
Luke moves over Vader and holds the blade of his sword to the Dark Lord's throat. The Emperor watches with uncontrollable, pleased agitation.
The Emperor: Good! Your hate has made you powerful. Now, fulfill your destiny and take your father's place at my side!
You can also look at his eagerness to replace Dooku with Anakin in Revenge of the Sith:
General Grievous: But the loss of Count Dooku?
Darth Sidious: His death was a necessary loss. Soon I will have a new apprentice, one far younger and more powerful.
We don't know exactly how Palpatine planned to handle the politics of the Separatist movement had he not found Dooku but we do know he had no issues running the show from behind the scenes. He did, after all, manipulate the Trade Federation into getting the ball rolling with the help of Darth Maul. But we also know he had no qualms with casting aside an apprentice when better opportunities arose. He may have still crossed paths with Dooku and manipulated him into killing Maul.
It's easy to hypothesize, though, that Palpatine's plan for Maul would have looked sort of like his plans for Anakin. Darth Vader was probably less chaotic than Maul but Vader's role as Military Hand of the Emperor would have worked just as well for Darth Maul.
I like to think that Darth Maul was chosen simply out of convenience. It is explained in the Darth Maul: Son of Dathomir comics that Darth Maul is actually the son of Mother Talzin, leader of the Nightsister clans on Dathomir. It is revealed that Sidious originally intended to make Talzin his apprentice after promising her an exchanging of dark side secrets between himself and Talzin, however Sidious betrayed and abandoned Talzin in favor of the child Maul.
Sidious would have no doubt sensed Maul's potential power as the son of Talzin, a noted powerful practitioner of dark magic. It is because of this that he opted to abduct the young Maul.
What I mean by "out of convenience" is that the son of a powerful force user, a relatively uncorrupted, young mind full of potential, was readily available for Sidious to make use of. Sidious, being the opportunistic mastermind that he is, took the boy for his own.
TheIronCheek also brings up the excellent point that Sidious has almost no loyalty to his apprentices, and simply goes with what is convenient at the time. This is even further evidenced by the statements above, as Sidious previously planned on making Talzin his apprentice, but instead favored the young Maul.
My reading indicates that "Darth," Maul was never a true lord of the Sith, nor a true apprentice of Sideous. I claim that Dooku was Sideous's true apprentice before Maul died.
According to Wookiepedia, "He[Dooku] left the Order, becoming one of the Lost Twenty.[2] He then regained his family's wealth and the title of Count of Serenno. Dooku was then approached by the Sith Lord, Darth Sidious, who asked for his help. Craving power, Dooku joined him and was given the Sith name, Darth Tyranus.[6] As Tyranus, Dooku arranged the death of Jedi Master Sifo-Dyas by contacting Lom Pyke of the Pyke Syndicate to shoot him down. Dooku was then given Sifo-Dyas's body. However, Dooku was unaware that the Pykes had captured Valorum's aide, Silman, alive.[15] On one of the moons of Bogden, Dooku then recruited the bounty hunter Jango Fett as the template for the Clone Army Sifo-Dyas ordered from the Kaminoans." from http://starwars.wikia.com/wiki/Dooku
This indicates that Dooku was in the employ of Palpatine while Maul was still alive, though I'm not entirely sure that this is the case. The fact that the clone troops "were completed within a decade[1]—approximately ten years[7] after the Battle of Naboo[1]," implies that Dooku had been approached before Maul's death.
We have further proof that Sideous perverted the Rule of Two in EU canon based on Starkiller, Mara Jade, the other hand of the Emperor, and others. Using an insane murder machine as an assassin is not out of character for him. I will also claim that Sideous did not truly pervert the Rule of Two by claiming to have multiple apprentices as long as he didn't teach them anything appreciable. Not even combined could his later force users face off against him (except possibly Starkiller, but that was not part of his plan).
Based on Maul's journal, and Darth Maul: Shadowhunter, we see a sentient without much training in the force aside from assassination techniques. We know that he spent a great deal of time building a lightsaber, but he laments the lack of time spent in personal training. He is taught more often by droids or told to meditate by himself. This is reminiscent of Starkiller's training at the hands of Vader (who was definitely not a true apprentice) and the techniques are similar to what Mara Jade was taught (also nto a true apprentice). In order to become a true Sith Lord capable of defeating Sideous and continuing the RoT, Maul would have needed far more control over force techniques rather than just his lightsaber. His stealth and rage however, make him feel better suited to the Assassin or Marauders mentioned in Darth Bane: Path of Destruction, and KoToR II. Finally, Palpatine's political plans were not spur of the moment. He knew that he was going to be a senator, otherwise he would not have spent so long on that persona. A tattooed Zabrak with anger problems with no political training would never have been able to take over any political machinations Palpatine set up.
In summary: Sideous never intended Maul to be a true apprentice and was instead using him as a skillful killer, OR Sideous was perverting the RoT because he didn't want to ever be replaced.
