In the past, when there were 5000 tix left, and they got the extension, it was just so they could sell as many as possible before Ralph called around to big sponsors and asked them to buy the remaining tickets to give to underpriveledged kids. TOPS used to do it, M&T Bank was a regular, etc, etc.
I would say the game will sell out, and it will be on TV. The networks want to show the game, thats why the league gives the extention. If there were 20000 tix remaining they wouldn't get the extension.