l'm thinking that too. Especially now with Yamato leaving Momo, I feel Kinemon is far too weak to protect Momo. I think Oda wants Sanji to protect the father/adoptive son duo.
Sanji has been only caring about them since the raid started
And his interest in there predicament was set-up since PH.
As of now....I call bullshit on Sanji not going to them eventually. He's only been caring about them since Onigashma part started.
976 -989 = Only cared about Momo
990 -1005 = Only cared about Kinemon
1006 -1012 = Wanted to help both, (chose Momo tho).
Sanji will come in clutch and save both of them from King is what I'm thinking.