All of these need some help. This makes sense: Do it and you will face the consequences. Or "if you do it, you will face the consequences. You will have to suffer the consequences or the results of your act. It sounds like this is a risky thing to do. This really might be a warning, "you had better not even think about doing this act".

I think that this one sounds more natural: "Do it, and face the consequences" But I also think that only your third option is incorrect. The first, and second one are correct, but sound weird.

If you do it, you must face the consequences. or If you do it, you will face the consequences.(stronger in tone than the above) The ones below are stronger in tone than the first one as well. Do it and face the consequences. or Do it and you will face the consequences.

I think both the first one and the second are correct.