The fans and media had been pressuring Ross to fire Ireland since 2011. That included two planes flying around games with banners. It also included a confrontational moment between Ireland and a fan. Ross still almost kept Ireland this year.
I don't think Ross is one to succumb to outside opinion on firing Philbin, especially when the Wells report clears Philbin of any wrong doing. Now some fans and media are using grey area to blame Philbin for not knowing, but there are plenty of people who back up the idea that a head coach probably wouldn't have known what was going on. The guys on NFLN made good points why a head coach wouldn't know and Bryant McKinnie who was in the locker room went out of his way to tell people that Philbin deserves no blame.
What that all means is that while some think Ross should fire Philbin over this incident, there are just as many who don't think he should. This offseason is already in full force, so making a head coach change at this point would just make this situation even worse.
Ross did set this season up that he can easily pull he plug and clean sweep next January if he wanted to. He aligned Hickey's contract with Philbin so they now appear tied together. If he clean sweeps next January, Ross will likely have his pick of "star" head coaches.