Considering how the other two Yonko showed up and showed out, Luffy and Mihawk (who's the de facto leader of CG with Buggy being a figurehead) have to match their feats or even outdo them if possible, and they can do this by defeating Admirals.
But even if Kizaru manages to escape and retreat, it would make no sense for Luffy to have to get saved or lose here, especially right after becoming a Yonko and telling Issho that he's done running from Admirals.