I have been in this situation a few times and it never works out. YOU ALREADY HAVE STATED THAT YOU DO NOT WANT TO WORK THERE. The agreement that you are about to sign, even if written by the best attorney that money can buy, will not be able to set the work rules. What happens if the schedule is such that you are now needed in a "special" project that requires you to work under the most limited time requirements that you have ever heard of? How about being assigned the most "interesting" tasks, in COBOL? Or you must manage the group that needs your "unique" leadership values?
If you are willing to work 28 hours a day, and move backwards ten years and do the work of the group, otherwise you are marked as NOT DELIVERING on your promise, stick around.
Ask yourself this question: If you are so valuable as to be worth 10% of the company, why did the owner wait until you were ready to walk? I have been at all levels, and when management believes that someone is worth it, they quickly make sure that you are tied in, way before you are ready to walk. You are valuable, but you are valuable because you have something that management feels it needs now, not long term.
Become a consultant, up your rate by 25%. And make sure that you a second job lined up, as you will quickly find out how "valuable" you are. IF I am wrong, you just got a nice raise.