This is how they came back to DC World in Ryan's Quest 2.
They are back in Gothem City and they saw Heartless coming attacking the Civilians
Ryan: We have to save everyone!
They saw Superman and the others
Superman: Oh. Robochap and Zoro.
Sora: That's Sora and Ryan!
Batman: Will you help a superhero or not?
They are fighting the Heartless and they defeated them
Wonder Woman: I wonder why they here again?
Batman: Well, it's seems that Laxm has returned and trying to take over the City.
Superman: It looks like you're right, we have to find him.
Sora: Let's go!
[They went off and they found him]
Laxm: How long you took since I abandon the name Mal?
Ryan: Out with it, Nobody, where's Meg, Kairi and the Others!?
Laxm: I don't know where they are. My boss Vixyner told me.
They are fighting him and thy defeated him and now he's fading away
Laxm: No... No! It's MY time, Roxas and Ranyx! MIIIIIINNNNEEE!!!!!
Ryan: (Shivering) I don't want to remember him ever again.
Sora: At least, we save the City from him.
Ryan: Lucky us. It's time for us to go and find their Stronghold.
Batman: Good Luck.
They left this World