Why am i thinking there is no fight between Coby and Hancock
You may be right
In my mind oda isn't going to have any of them lose to the other. He will keep both of their strengths about even for build up with both characters.
We will be able to upscale Coby without being able to down scale boa
I see the fight being interupted by a communication to Coby from xdrake. With koby hearing the announcement of strawhats luffys defeat to kaido. Once this is brought up boa will also hear.
Upon Coby noticing this they will form a truce with him allowing her amazons to escape the island. She them goes with Coby after finding out his history with luffy. The marines call into HQ stating that captain Coby has captured boa. He then gets a promotion to the position of vice admiral. However instead of turning her in he allows her to escape giving him the excuse to capture. However it's a plan for both of them to escape to then travel to wano to help luffy.
Boa wants to help luffy. Coby does as well. However he also wants to assist and to gather Intel and to help stop the alliance of the yonkos since that's very bad for the marines. Also with him being their he will be able to vouch for xdrake. Thus allowing to return as being a regular marine agaon