The publisher could not go ahead and just publish the book without your agreement because, whatever rights the publisher might have to its contributions to the book, it has no rights to your contributions to the book which, as the author, constitute most of the book. That being said, if the publisher has contributed value to the book the publisher may have a copyright interest of some sort in the completed book and may try to claim damages from you if you publish elsewhere.
Given that, you would be well-advised to suspend the work with the publisher and consult with a competent copyright law attorney to see what your options are.
My answer does not constitute legal advice and may not be relied upon by anyone for any purpose and does not constitute an attorney/client relationship or an offer to form such a relationship. This disclaimer is intended to be fully compliant with the requirements of Treasury Department Circular 230 and the terms thereof are fully incorporated by reference. If you wish to consult with me please contact me at dana@nytaxcounsel or visit my website at www.nytaxcounsel.com
Your best course of action is to have a consultation with a lawyer who specializes in publishing. Trying to do this through an intertnet post is a big mistake. Don't be penny wise and pound foolish.
I am a former federal and State prosecutor and now handle criminal defense and personal injury/civil rights cases. Feel free to check out my web site and contact me at (212) 577-9797 or via email at Eric@RothsteinLawNY.com. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. The above answer is for informational purposes only and not meant as legal advice.
No he cannot publish a book without a contract entitling him to do so. However, he may claim a quantum meruit and/or unjust enrichment theory to get paid for the reasonable value of the services provided.
Ryan Finn * 518.213.0115 * Rfinn@hackermurphy.com * Referrals are the highest form of compliment * Hacker Murphy serves clients throughout New York State and always pays referring attorneys a reasonable referral fee in contingency cases