Even though that the Cincinnati Bengals have declared a sellout on Friday, tickets still remain that are other not required for the team to announce an official sellout. Joe Reedy of the Cincinnati Enquirer writes:
A limited number of tickets — from visiting-team returns and in obstructed-view areas — remain available and may be purchased by calling the Bengals Ticket Hotline at 866-621-8383 or through Bengals.com.
So if you're looking to score tickets for the game, there are options. Or you could purchase through one of the many ticket agencies.
Also during Reedy's above posting, one thing that caught my eye without realizing it. It's been nearly two years since the Cincinnati Bengals last for extension before declaring a sellout. Ironically that game was against the Miami Dolphins on October 31, 2010.