I don’t know, it seems to me that leaving Repliku was his final farewell to this character. He entrusted the future to Riku.Nobody is ever really gone in KH. Replica Riku also still has Way to Dawn which was something of a hint about him eventually getting the chance at being his own person.
Yeah, exactly. 2.8’s credits came out a long time ago. That is plenty of time for Nomura to change his mind. Also Roxas and Namine never interact at any point in KH3, and instead they decide to focus on Namine and Replica Riku’s connection and make that a focal point of the scene when Riku reaches out to Namine. That was meant to represent the promise Replica Riku made to Namine.
Yes, and Repliku's feelings are largely based on Namine's false memories. The same Roxas and Namine, regardless of the fact that they are nobody Sora and Kairi, built their communication separately from them.