Remember in WCI, when the revenge army was coming after Luffy and Nami post Cracker's defeat. Nami channeled the storm energy to devastate the revenge army. This happened in-between panels.
I believe a similar thing could happen. Nami makes her way outside, and with BM channeling around all that electrical energy. Nami could have access to a far amount of this storm energy. All our Storm Princess has to do is redirect it on to Ulti and Page-One.
I believe Zeus returning has to wait until BM piece has been knocked out of the ring not necessarily defeated.