なれ is the imperative form of 成る. とも is a bit classical. It's equevalent to ても/でも in modern Japanese(in this case, にでも, as I rephrased).
大辞泉 says that this と is originally from the quotation と.
とも[接助副助終助]の意味 - 国語辞書 - goo辞書
どうともなれ basically expresses that he don't care if the situation goes either way (= what happens).