I think he was gone the moment he said at the hearing that “it makes (him) slightly nauseous to think that my actions may have affected the outcome of the election.”
Whatever that thought represented in his mind, the most obvious meaning is that he felt slightly nauseous that he did something to help Trump and to defeat Clinton.
With that political bias made evident, he was in no good position to continue to oversee investigations of a political nature related to either Trump or Clinton.
It could be surmised that his greatest loyalty was to Obama and that would be even more of a good reason to let him go.
I think he was gone the moment he said at the hearing that “it makes (him) slightly nauseous to think that my actions may have affected the outcome of the election.”
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That and the fact he just LIED (Oops, he made “misstatements”) to a Senate Committee this week also was grounds for immediate dismissal.