The correct option is
B Until you finish
The word, "until" means "up to the time that".
The given sentence means the same "Upto the time that you keep the work unfinished, you won't be given leave". It doesn't communicate when the listener will be given leave. A better way of saying the same would be "Until you finish the work, you won't be given leave". This means: "The work must be finished. Upto that time, you won't be given leave". Here, it is implicit that once the work is finished, the listener will be given leave. Hence, option C is a better substitute for the given sentence.
Option A: The sentence, "Until you must finish the work, you won't be given leave is incorrect. This is because the word, "must" is used in an imperative sentence to communicate an instruction. The clause starting with "Until" communicates a condition and not an instruction. Hence, this option is incorrect.
Option B: The sentence, "Until finishing the work, you won't be given leave is incorrect. The word, "until" is followed by a clause in simple present or simple past or present perfect or past perfect tense. It cannot be followed by a present or past continuous tense as it indicates the time upto which a particular event happens/ happened. However, "finishing" is in present continuous tense. Hence, this option is incorrect.
Option D is not applicable as option C is correct.