He won't stop until it's finished =? Not until it's finished, will he stop.
I think the above-mentioned statement is true.
Do you confirm? The sentence was partly made up by me.
The two phrases are equivalent, but no native English speaker would ever say "Not until it's finished, will he stop".
Except for Yoda, of Star Wars fame - but then, he probably wasn't a native English speaker....
I'm not a teacher of English, but I have spoken it for (almost) all of my life....