We had our combo interview on 11/07 and was approved for I-751 as well as the N-400. It was immediately updated on the USCIS Website that we were approved and should receive notice in the mail which we received yesterday. However the noticed stated he won't receive a 10 year green card since he will be having his oath ceremony for naturalization. I can guarantee your I-751 was approved because you wouldn't be having an oath ceremony. BTW, congratulations!
Sidenote: Be sure to update your timeline.