Prior to the official release of this story arc, Ahsoka provided an account of what happened at the end of the Siege of Mandalore when Order 66 was executed. Now, we get to see it physically.
Chekhov's Gun: Rex did not execute Order 66 because he was not brainwashed as a result of the fact that he listened to Fives and removed his chip.
Dramatic Irony: Had Palpatine waited a little longer to execute Order 66, Ahsoka and the 332nd would've killed Maul, which would've saved him some trouble later.
In the End, You Are on Your Own: Ahsoka, a former Jedi, and Rex, a clone trooper, are left on their own to survive after the execution of Order 66. When they leave Mandalore, they go their separate ways.
Anakin:[walks in with Obi-Wan] Alright, Rex. What's so important that you brought us all the way back here for? [Anakin and Obi-Wan express shock when they see Ahsoka and Bo-Katan on the other side of the holocall] Ahsoka:[turns around to face Anakin and Obi-Wan] Hello, Master. It's been a while.
Sudden Downer Ending: From Ahsoka and Rex's perspective. While the Siege of Mandalore looks to be a winning fight, things aren't doing well at home. The siege looks like it's about to end now that they've trapped Maul... only for Order 66 to be executed, forcing Ahsoka and Rex to flee and go into hiding while Maul also gets to do the same.
True Companions: The 332nd, a part of the 501st that is given to Ahsoka to fight at the Siege of Mandalore, redesign their armor to resemble her markings. It just shows how much they respect their sister-in-arms and how much they've missed her.
Ahsoka is placed in charge of the 332nd, a portion of the 501st.
Ahsoka, as the Republic's liaison to Mandalore during the siege, grants Bo-Katan the position of leadership to Mandalorian Space. Unfortunately, it doesn't last, as the siege had left Mandalore too weak to stand up against the arrival of the Empire, resulting in Bo-Katan's leadership being taken.