Here is what I believe the NFL will do
Bengals-Bills won't be made up. Under any circumstances. The league will not push the playoff schedule back a week in order to play one game next week.
The MNF game won't be declared a tie. The Bengals won't be awarded the win. The Bills won't forfeit. The game simply won't be played. The two teams will play 16 games, while the other 30 teams will play 17.
The reality is there is no perfect solution. Some team(s) will come out on the short end of the stick.
What happens if the game is not made up:
The Bengals win AFC North....no matter what happens Sunday.
If they beat Baltimore they win the division by 2.5 games (Bengals 12-4/Ravens 10-7).
If they lose to Baltimore they still win the division by .5 game (Bengals 11-5/Ravens 11-6).
The Ravens will be livid. Understandably. There is a chance they could beat the Bengals twice and yet lose the division by a half game because the Bengals played one less game.
The NFL won't announce that MNF won't be made up until AFTER the conclusion of games on Sunday. Announcing the decision prior would eliminate any drama of the AFC North title.
What's left? Seeding
I'll try to keep this as simple as possible.
No 1 seed:
The Bengals would be eliminated from contention for the No. 1 seed if MNF is not made up. They would not be able to catch Kansas City (13-3), no matter the result of Chiefs vs Raiders on Sunday.
No. 2 seed:
The No. 2 seed would still be in play for the Bengals.
The Bengals could edge out the Bills for the No. 2 seed IF the Bengals beat the Ravens AND the Bills lose to Patriots.
That would leave the Bengals and Bills both at 12-4. The Bengals would win by the 5th tiebreaker...Strength of Victory (combined winning percentage of the opponents a team has beaten).....
The Bengals currently hold a .483-.479 advantage in SOV.
That's my best guess.
There will be a quiz on all of this.