Hi,
As another said, please tell your friend to talk with a Lawyer! If they are separated, the Lawyer will know what to do, legally. Such as, filing a separation Agreement (if needed in their State), and what to do after that.
It seems to me that anyone who would use a dead person's identity to get married, for whatever reason, is not the type of person to marry. After finding out, your friend made a good decision to separate. Best of luck.