Personally I probably would have just let him ride out the season (it appears to be a bit of a lost cause at this point - bottom of the table with most remaining games on the road), and then make the change. He had some bad luck with injuries/players being out (Childress, Markovic), integrating others on the fly (primarily Harrington), and what appears to be a general dysfunction within the team.
Part of that last point potentially is on Cotter, but it is the team he was given. In saying that, his management in-game seemed to be puzzling at times (in my opinion, and granted I am no coaching expert) and he appeared to be unable or unwilling to make adjustments, and most certainly appeared unable to light a fire under his players at times (a lack of leadership perhaps?). The players at the very least seemed unaware of what they should have been doing, and an overall lack of purpose for stretches, which I imagine a coach is largely responsible for.
Personally I'd be happy just to see effort (a la Townsville, despite being overmatched on the regular) and a semblance of direction, clear & concise.