This is really a divorce/family law question - the rights you each end up with regarding each other's retirement accounts will be decided through your divorce, where it is a matter of what is considered fair under the divorce laws. Basically, everything is up for grabs and if you can't work it out in a property settlement, it will be up to the divorce court to decide. Discuss this with your divorce lawyer.
This answer is not intended as legal advice or to create an attorney-client relationship between you and me. This is intended for general informational purposes only and should be used only as a starting point for addressing your legal issues. It is not a substitute for an in-person or telephone consultation with an attorney licensed to practice in your jurisdiction about your specific legal issue, and you should not rely on this answer. Also, because of IRS regulation, any discussion of tax issues in this answer was not intended or written to be used, and cannot be used by any person (i) for the purpose of avoiding penalties that may be imposed by the Internal Revenue Service, or (ii) to promote, market or recommend to any other person any matter or course of action. You should obtain a formal written opinion if you want to be able to use it for either of those purposes.
The general rule in Michigan is that each Party is entitled to one-half (50%) of the other Party's retirement benefits that accrued during the course of the marriage -- that includes BOTH your defined benefit plan (your Pension) and your defined contribution plan (your 403(b) Plan). The issue of how to handle a house that is "under water" is extremely complex -- IMHO that type of "debt" should be treated differently than a "regular" debt like a mortgage or credit card debt. I would kindly but strongly recommend you consult with a local Family Law lawyer like myself to assist you, and to present all your defense to his claim concerning the under water house. I wish you all the best of luck. Warmest regards, Matt Catchick.
A weekly guide with tips and legal advice for each stage of the process.