There are two versions of the John Carpenter film. In the original theatrical release, there's an ending such as you describe. In the other, there's a further bit where there's voice-over and a repeat of some of the opening landscapes, etc. It really weakened the punch of the original ending which, as you say, was left open... were either of them? If so, would this whole thing start all over again... only worse (being out in the world at large)? And, for that matter, the possibility that sharing the bottle spread the contagion... and so on.
For all its over-the-top (at times) effects, it really was a rather good adaptation of the incidents (though not the underlying philosophy) of John Campbell's "Who Goes There?", while the original is a different film, really; good, but quite a different proposition.