My N400 interview in Chicago was a combo interview, and I wasn't told ahead of time that it would be. It's definitely possible that you will get a combo interview too so I would prepare as though it will be. I had my combo interview on 3/14, my N400 application was officially approved on 4/8 and my i751 was approved on 4/11. I think they cannot approve your N400 on the day of your interview if you still have the i751 pending, or if you have a combo interview. I haven't heard about my oath ceremony date yet but hope it will be soon.
One thing to consider is that you can apply for an "urgent travel" passport within 5 business days of your planned travel, and I think you receive it on the same day. So long as your oath ceremony is at least 5 days before your overseas travel, you should be okay. This is what I'm planning to do as well.