The death certificate is only as accurate as the person who provided the information.  The divorce would not have been completed if he died two weeks after he filed.  There are implications to the estate tax, based on his marital status.  Even if the wife was not named as beneficiary, she is probably entitled to a distribution under state law, and it would be deductible if he was married.  

When in doubt, tell the truth.  MFS isn't going to cost him anything anyway; he's dead.