If it does not harm you to do so, let him do it. His divorce, let him own it. I have first-hand experience in not being able to push a person where they are unwilling to go.
Unlikely this legal insurance will cover much. Mediation is a voluntary process. There is no harm in going and see what you can resolve. Before you do, take some free consultations with divorce lawyers (ones who only handle domestic issues), get an idea of what the issues are in your case and how the court is likely to resolve matters. Find one you like. Have them attend the mediation or be on standby or review anything before you sign it or agree to it.
Take it one step at a time. Don't do anything that you believe to be wrong or not in your best interest. Don't try to be nice in the hopes it will bring him back. It doesn't work and you don't want to harm yourself.
