OP bring up a lot of good points, but I haven't seen this one brought up much. Kliff has 1 year left on his deal. It's generally not a good idea to go into a season with a lame duck coach...although we could.
So if the choice is fire Kliff or sign him to an extension, it really makes the choice more difficult.
I'm not sure keeping him next year as a potential lame duck does anyone any good. But if we extend him, even as a gesture, and he craps the bed again...now we are on the hook for more dead money.
I would fire him and make a serious move for Flores, Bowles, Harbaugh, or the Bills OC.