Warning! SPOILERS for Star Wars: The Clone Wars season 7, episode 8 ahead.
Maul has returned in Star Wars: Episode III - Revenge of the Sith, the animated series is quickly approaching the events of the third and final prequel movie.
Thus far on The Clone Wars season 7, the Battle of Anaxes has been a decisive victory for the Republic, focusing largely on the various Bo-Katan Kryze and her Nite Owls. All in all, it's been an exciting adventure that's allowed Ahsoka to demonstrate her skills even when she's without her lightsabers, but with the return of Maul, the true purpose of these recent Clone Wars season 7 episode has been revealed.
In Star Wars: The Clone Wars season 7, episode 8, "Together Again", Ahsoka discovers that the Maul fled back to Mandalore with Death Watch after the Shadow Collective disbanded, he's likely needing to gather supplies to hold off the rebellion led by Bo-Katan.
Ahsoka overhearing Maul's conversation is what reintroduces him back into The Clone Wars story, establishing that he is once again consolidating his power for a nefarious purpose. It also explains why Ahsoka needed to tag along on the Martez sisters' poorly thought out smuggling mission, revealing to her first that Maul is up to something. But Ahsoka's season 7 plot also brings her back into with Bo-Katan, who follows Ahsoka back to Coruscant with a proposal that she work with them to defeat their common enemy - Maul.
Bo-Katan's request of Siege of Mandalore, a conflict that sees Republic forces lay siege to Mandalore in an effort to oust Maul. Chances are, it's Ahsoka's involvement in Bo-Katan's rebellion that will catch the Republic's attention - or more specifically, Anakin's, who will send along Captain Rex and company of clone troopers to assist her. In which case, having Ahsoka learn about Maul's new endeavors and reunite with Bo-Katan is this episode is how Star Wars: The Clone Wars season 7 is setting the stage of the Siege of Mandalore.