"What if there were no star in the sky?" also works even if you want to use the subjunctive.
Note that not all native speakers of English use or prefer this type of construction. Also, this use of "were" instead of "was" is sometimes now called irrealis and considered separate from the subjunctive (which is then used to refer only to constructions like "it's important that you be here early tomorrow").
It may found in usage, but then so is "liek"..
At the end of the day there is accepted grammar and there is actual usage.
If you ask people for the accepted grammar they will give you something most people accept. Which is not "What if there were no star in the sky?"
It doesn't really. I'd immediately think "what about the rest of them?". "Not a star" works, but that's because it is made indefinite by the article. I wonder if the point here is that in English, dropping the article implies "the" in a way it doesn't in other languages.