Even though Maul is dead, he was instrumental in the affairs of the Mandalorians - which Boba Fett has been confirmed to be - and he died on Tatooine where Boba now rules. Also, if Boba Fett intends to maintain his new power position, he's going to have competition.
Darth Maul is a Zabrak Sith Warrior from Dathomir who is abducted by Sidious as a child and trained in the ways of the dark side of the Force. He mortally wounds Jedi Master Qui-Gon Jinn during the Battle of Naboo before being bisected by Qui-Gon's apprentice, Obi-Wan.
Plagueis, however, was fully aware of Maul's existence, and supported Sidious's decision to train him. The primary reason for Plagueis's support, despite the violation of the Rule of Two, was that Maul was trained to be expendable.
Maul's force sensitivity, intensive training, and knowledge of Boba's tricks would limit the effectiveness of long-range or surprise attacks, and up close and personal, Fett is no match for the Sith.
As much as fans would probably want to see Luke win this matchup, it is pretty unlikely. Luke is strong with the force, something Maul struggles with. He is so focused on his hatred that his Force sensitivity evades him. But when it comes to lightsaber combat, Maul is the definite winner.
Overall, Dooku was far more equipped to become a Sith Master than Maul was. Had he managed to overthrow Palpatine, Dooku would have been able to use his position, combat abilities, and dark side Force powers to take his place on the throne Palpatine had carved.
Regardless, based on the season 7 of The Clone Wars, and the fact that Darth Maul was aware of Anakin Skywalker's future and his role as the Chosen One, it is very likely that Darth Maul indeed feared Darth Vader to some extent, and preferred to avoid a direct confrontation with him, at least, on his own.
Following Qui-Gon's death by Maul's hand on Naboo, Dooku visited Palpatine in distress about his apprentice's death, hoping to have one day made Jinn an ally while also directly stating he knew of Maul's existence.
As the son of Mother Talzin, the Zabrak male was taken from a young age by Sidious to act as his impressionable apprentice. The boy was raised as Darth Maul, a name he carried throughout his life. In Legends, it was insinuated that he was born "Maul" before attaining the honor of the "Darth" title.
The resulting siege by a Mandalorian-Republic joint force ended Maul's rule over the planet. The Republic subsequently appointed Bo-Katan Kryze, the leader of the Mandalore resistance, as Regent of Mandalore.
Sidious revealed to Maul that he did not intend to kill his former apprentice, as he still had use for Maul; it was Sidious' hope that Maul would lead the Sith to Mother Talzin, Maul's mother and the leader of the Nightsisters, so she could be eliminated as a potential threat to the eventual Sith rule of the galaxy.
Anakin Skywalker's birth mystery is solved - his mother, Shmi Skywalker, reveals that there was no father and she can't explain what happened. Qui-Gon Jinn believed that the Force itself created Anakin in Shmi's womb, making him the Chosen One who would bring balance to the Force.
While seemingly killed in Return of the Jedi after falling into a sarlacc, he has since appeared in Star Wars media set after the film, confirming his survival within the new canon, portrayed by Temuera Morrison.
But, let's be honest, he definitely found out. Order 66 was such a widespread thing that most people knew about it. Surely, Boba Fett, being a famous bounty hunter, would've heard about the fall of the Jedi Order—if not, Mace Windu's death specifically.
The Mandalorian super commandos consisted of Death Watch soldiers who were loyal to the renegade Sith Lord Maul, leader of the Shadow Collective, who killed Pre Vizsla and took control of the planet Mandalore during the Clone Wars.
Palpatine saw Maul as a pawn and used him to his advantage, but never considered him a direct threat to his life. Palpatine didn't care about killing Maul for his failure, showing his carelessness and disregard for attachments ultimately led to his downfall.
Maul most likely knew Sidious' double role as Palpatine and Sidious when he served as Palpatine's apprentice. He definitely knew about Palpatine's goal of creating a galactic empire ruled by the Sith. Maul knows that Sidious is the Emperor.
During Star Wars: The Phantom Menace, Darth Maul had no clue about Anakin and dismissed him as a child following the Jedi around. But with Maul's return during the Clone Wars, he likely found out about Anakin through his obsession with Obi-Wan.
In a non-canon story from the pages of Star Wars Tales #9, Darth Maul was resurrected to fight Darth Vader to the death. Ultimately, Darth Vader was named the victor for a pitch-black reason: He hates himself more. In the main Star Wars canon, Darth Vader and Darth Maul never met, let alone fought.
It's already been shown in the source material… more than once… that Darth Maul is not on Darth Sidious's level. Every time he dueled Sidious as his apprentice (in Legends) he got easily defeated.
