I do agree that it would be VERY difficult to miss the playoffs at 11-5, but I do see a couple ways.
1) DAL-PHI tie, then win out, both going 11-4-1, DET wins out (12-4), GB only loses to DET (12-4), SEA beats us and at least one other team (11-5).
2) DAL beats PHI, loses to IND, beats WSH...