First off, I agree that the tense should be the past "might have been."
But on a broader level, that whole "that it might be implied" clause seems problematic to me because it appears imprecise what "it" is referring to. What exactly is the antecedent? Of course one could say that it's the entire sentence "They wanted her to leave," but that verges on being unacceptable in my opinion to make an "it" refer to a thing so hazily. Plus "that" is located so far from "so" in the construction, which doesn't help matters. I think it would be better for one to maybe replace "it" with something like "their wish"