I like Vivi but i would prefer if she return just when the SH go fight the WG.
We really dont need her in Egghead as the arc is basically done plotwise and Elbaf is set to have so many characters and plots already that adding all this Vivi/Nefertari would be good for nothing besides blobing the arc.
Would be good If the SH get hints from the Nefertari significance from Ohara Library in Elbaf and then realize they need Vivi, as would be cool to have her there when we get the Void Century FB as probably Lili will be one of the key characters with Imu, Joyboy, the Kozuki leader and Poseidon.