That can not and will not ever happen because they are fundamentally opposed entities. The Libertarian party's core tenet is fuck you, I'm eating, and the Green party's core tenet is wait, I live here. Ne'er the twain shall meet. If we had a less-insane Libertarian party which cared about the environment, then you wouldn't need a Green party.
Wow, you have quite the narrow view of people don't you? I guess in your world people are just cookies that fit predefined shapes. Yes, all green party people are the same. All libertarians are the same. People are groups they're not individuals, that's an insane idea! Most libertarians I know (not the ones the media likes to snap up) do in fact care about the environment. It falls within their core tenet because they care about protecting the rights, liberties, and livelihoods of all individuals... hey, that includes the environment too because I don't want you to poo in my backyard or the air I breathe. The big difference between libertarians and green party is *how* they do it. That's where the chasm lies.