Agreed, but smearing him is one thing. NCAA violations are a different can of worms. If he is found to have committed NCAA recruiting transgressions, you aren't smearing him. Those would be his responsibility to answer for.
Tbe OP brings up a valid and very important question. NCAA investigations typically take years, not months, and nobody at NCAA HQ is going to speed ours up just because we want to fire a coach without having to pay his buyout. If you assume the school decides to fire him at the end of this season, it's likely the investigation isn't going to be over by then. If you wait until it's over, you could be waiting another season or even two until you know the results. Obviously the school can't keep waiting to make the call if committed to firing him. You either pay the buyout or you end up in limbo for some indeterminable period of time while he's still your coach.