OUCH!!!!!!! That is scary stuff right there..... Our IO interviewed us together, then offered me the opportunity to stay for wife's N-400 interview (Wife didn't want me to stay...LOL)
Then you have no choice. If you need evidence of status, you will have to contact USCIS and request a new ADIT stamp.
Note: you will still be a legal resident even after your current stamp expires.
20 days is short time between oath and travel. Your only hope is to get an emergency passport appointment after the ceremony. That has worked for some. I also think delaying the ceremony is risky.
I'm not necessarily recommending it, but another option is to wait until the 5 year rule kicks in. It is quite easy to apply. Then, if you have a combo interview, you'll be ready to show evidence.