Kaku won't fight the Strawhats anyway. All things aside, at his core he sticks to his morals as seen in Enies Lobby where he was genuinely sad he couldn't continue working as a simple shipwright.
He promised no harm after fighting the Seraphim and that's that imo.
Sanji is left woth either a Vice Admiral or a released Seraphim.
But the likeliest scenario is no fight for him here