Is your divorce finalized? If not included in it that he has to refinance or sell to get your name off the mortgage.
If it is finalized regardless of what the divorce decree states if your name is still on the loan and he defaults it is going to reflect on YOUR credit.
Also if he does refinance you may have $ coming to you if property taxes and insurance were part of mortgage payments.
Contact the mortgage company and let them know you want your half.