● You can critique it all you want and it won't change a thing. It's over. ● You can talk about it until you're blue in the face. It won't change a thing.
critique it all you wantは「好きなだけ論評する」、talk about it until you're blue in the faceは「いつまでも話す」の意味になります。
Second-guessing him/her/us/me won't help anything. It's over. 「彼のことを後でああだこうだ言ってもどうにもらないよ。もう済んだことなんだから」。