Formally Disproving Divine Command Theory

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Let's say that I am in a situation where someone is about to die. I have the opportunity to save their life if I lie though, so I do. According to the Bible, lying is a sin and therefore I am "morally bad" if we say the Bible is 100% correct morally.

For those Christians who say that lying in this case would have been justified, then it logically follows that Divine Command Theory falls apart:

p: there exists an objective moral code
q: lying is always wrong

First, we assume two things: p and "if p, then q". From this it logically follows that q, because if p, then q. For those of you who say lying was morally right in this case, it means you're assuming ~q (i.e not q). Here we have a contradiction where you're wanting to say q & ~q, which means that our conclusion must be one of our premises (p, if p then q) in the negated form; either ~p or ~(if p then q) because that way we avoid the conditions needed for this contradiction to arise.

Surely the believer will want to salvage p meaning that we must negate "if p then q". So our conclusion is therefore "it is not the case that if there exists an objective moral code then lying is always wrong". The problem is that the Bible asserts that "if p then q" but we have concluded that ~"if p then q". A contradiction arises which means we are left with questioning the validity of p as being a true statement, unless you wish to avoid this conclusion by simply saying you wouldn't have saved the person's life by lying.

logical fallacy.

we would first have to start with proving the bible "true" literally. That can't be the case, so using the bible to disprove the bible is as dumb as proving the bible with the bible.