An alien is deemed a "spouse" for immigration purposes, even though the parties to the marriage have ceased cohabiting, as long as such marriage was not contracted solely to qualify for immigration benefits. If the parties are legally separated, i.e., by written agreement recognized by a court, or by court order, the alien no longer qualifies as a "spouse" for immigration purposes even though the couple had not obtained a final divorce.
9 Fam 40.1 N1,6 Legal Separation Versus Marriage Termination
Based on the above, I believe your friend will be fine and should continue processing as "Separated" until the divorce is finalized. He shouldn't submit his form as "divorced" since there's no divorce decree in place corresponding to the date of when the form is submitted.