Namine and Xion had torments which related to the suffering of the people around them, that tied back with their own natures and guilt trips.
Roxas has the whole "my Heart belongs to me" and independent identity issues.
Axel... I donno. That's another good question. Watch Ven mess this up, alternatively, Axel's torment be tied to the Memories he lost of Xion.
Repliku had none of this. He never forgot anyone and he never related to anyone on such an existential manner. He was created by Data Vexen stole from Riku and had Namine duplicate Riku's Memories. This isn't like Xion who had Sora's own Memories and was considered a part of him. This isn't like Namine and Roxas and Axel who went back to become whole but due to the way they 'went away' are most likely still inside those people and thus can have their torments lessened - and have torments to begin with.
As far as we know, Repliku had nothing that belonged to Riku himself - only copies. This also means that unlike Xion, when he faded, he had no reason to be absorbed by Riku and thus, most likely no longer exists at all - as opposed to everyone else who need to have their torments lessened.
Not existing = no torment = no need to be rescued.