Yes. Do first check the USCIS website to see when is the next info pass appointment (sometimes there are openings surprisingly soon). If nothing's open, yes, go directly to the USCIS with your I-797c and try to get some documentation of the emergency. If the system shows that your biometrics have been ordered the Application Support Center may process you even without the biometrics appointment notice. Otherwise, ask to speak to the USCIS supervisor on duty, explain your emergency, and, again, try to document it. See if you can reserve your flight too (try to purchase refundable tickets) and show proof of purchase for the tickets. Good luck.