So sorry you're going through this. I'm sure it is rough.
I filed in October 2018, and since then have separated too. I'm in the middle of a divorce and it will be finalized by end of July if everything goes smoothly.
Since you're asking about notifying USCIS, I am guessing that you want to switch to waiver eventually? Personally I don't think you need to notify USCIS right now. If they get notification, they will probably send you a RFE and you won't have the decree ready. Other people please correct me if I'm incorrect - it won't be too late to change to divorce waiver at the interview, and that will buy you more time to have the decree.
