Reports on the Husker Mailing list indicate that the Maine game is not sold out yet. My expectation is that they are now selling the Maine tickets from the seats not renewed by season ticketholders. Maine may have returned a few tickets as well.
I don't think the sellout streak is in danger this weekend. They probably already have an agreement with a "booster of substance" to purchase any leftover tickets.
But, with over 6000 new seats available next year, the lack of interest in Husker tickets is a potentially disturbing proposition.