Everything that Darkstar has done after the highbreed invasion was the fault of Ben, Gwen and Kevin. Because Gwen went to Cooper to free Micheal from the null void. Knowing how Gwen finds Cooper annoying and a creep she must of really wanted to bring Micheal back very badly. Shortly before the highbreed invasion was over Micheal evaded the team and ran off quietly.
Even though Gwen offered to have him free from the null void for his help on the invasion. The fact he disappeared quietly was shady as hell. They should have gone after him and send Micheal back to the null void.
Then after Darkstar tried to use the Dominus Librium to drain Gwen and Ben's powers. Thanks to Kevin trusting him again. Then after his plans were foiled, they didn't got Micheal arrested by the plumbers or send him back to the null void. They only just procrastinate it.
Then Darkstar used what's left of the Librium to double cross the crew again. Kevin only just gave Darkstar a punch in the face only as a payback to when Micheal suckerpunched him. He still wasn't arrested or sent the null void. Allowing Darkstar to later steal
Charmcaster's Gwen's spellbook. This went on until Darkstar was arrested by the police with Charmcaster in disguise.
Finally, the Plumbers has arrested Darkstar after he got out from Charmcaster's bag. At least a year after Gwen asked Cooper to free Darkstar.