There is no possible way you fire Flus in the season barring like a scandal. He isn't awful - but he's also not great. If you had Kingsbury or something and you were convinced you had the greatest thing since sliced bread (not saying Kingsbury is that - he had his flaws as a HC with Arizona - but to his credit he's doing an excellent job with Washington) than I could buy it.
But if you just canned Flus mid-season, what are you going to do, hire Waldron as the HC? Talk about spiraling out of control. Flus is bad out of byes - but he's also been pretty good at keeping his team focused following a loss. I still go back to - you had mediocre in-house and could have hired great (Harbaugh) and they passed.