You see, I think it's going to be Franky who will replace Jinbe in the fight against WsW, and I have a lot of reasons for that.
Jinbe vs WsW might be 20 chapters long, but all of them were off screened. The sheer fact that Oda has been very neglected of it means, that the fight itself isn't the final fight for Jinbe.
I have to point out, that it is more than possible for Jinbe to fight against Jack after defeating WsW. We've seen the beast pirates losing and coming back again and again, so based on that, I do believe that Jinbe might actually defeat WsW and have enough strength to finish off heavily and severely wounded Jack. I mean think about it, Jack has been already defeated by Nekomamushi and Inuarashi, he's been wounded pretty badly and is now fighting against Inuarashi without fully recovering. It would be quite unfair towards Jack if fresh Jinbe fights against him. So, what if Jinbe vs WsW is simply to make these two equally damaged? I think that's what Oda is planning.