Is it ethical to submit the final version of a paper after acceptance when coauthor refuses to agree to submission? Here is my case:

I wrote a paper and invited a post-doc to help me edit it. As the post-doc is much better than me, the post-doc changed a lot of content (nearly all, but without changing any idea). According to this contribution, the post-doc stands as second author. The post-doc agreed on the paper, then we submitted and the paper was accepted. After that, the post-doc claimed to be the main contributor, threatened to withdraw the paper (personal-conflict) and really did so. But the editor of the journal refused the withdraw request and asked me for final version. Even so, the second author kept on claiming that I don't have the right to submit the final version. In this case, is it ethical to continue the publication process?
I checked the authorship guidelines of the two most important computer science societies, IEEE and ACM. IEEE's guidelines have a clear answer to the question, although I wish it was a different one, given the unfair situation the post-doc has put you into:


  "Each individual named  as an author must approve the final version of the article as  accepted for publication, including the references." (Source: Sect. 6, "Author Responsibilities")


In the case of ACM, I didn't find a direct answer. The closest statement I found was the following:


  "Once a submission has been accepted, [...] ACM expects authors to speak with one voice even if there are multiple authors." (Source: "Processing of accepted works")


(Not a particularly helpful statement anyways: there are certainly situations where an individual author would behave ethically by not speaking for all authors, like whistleblowing).

In any case, you should look up the authorship guidelines of the journal where your paper was accepted - they might have yet another relevant policy for your case.