I was pondering this very question this morning. Not because a scenario has presented itself, but just a general thought of whether or not a lie is in fact sinful if it is done with the right intent. The truth prevails, but one must consider in acts of war when someone uses a decoy isn't that a form of deception? Is this just wise strategy or is this a sin against God? More often than not it seems that the intent behind the heart is the root of the problem. Even with lust Jesus went to the heart rather than the deed, not that one can commit fornication in purity.
That is a thought to consider, are there any other sins, besides lying, under certain circumstances that the absolute morality behind God's commands somehow waver? Take fornication, for example, and sorry if it sounds crude but say that a person is given the option to lay with another man and it could end a war. No bloodshed, no innocent lives or children dying, and no destruction beyond the temple of the one laying with another. This person who makes such a sacrifice for a nation, for peace, has this sin of fornication somehow been justified or rather should the burden of death be on their mind all their life had they only given themselves (if they rejected the offer)?
VVe can keep doing this with all the different sins and put them under circumstances that, maybe, allow for some breathing room. VVhile God's standard of righteousness is perfection, we must remember that God is a gracious and merciful God. He knows all things, including the heart. His grace is sufficient, not so that we may sin but because we do sin. Jesus paid the penalty for our sins and so we are justified before God on the basis of His mercy.
This question of whether a particular sin is justified under certain circumstances, while an intriguing thought, must be kept in line with the truth of Christ and Him crucified. God isn't ought to get you, but rather wishes have a relationship with you that is already possible through Christ. Is lying okay under certain circumstances? It seems to me that one is willing to sacrifice their self for the sake of others. If lying as a sin leads to death and one chooses to lie for the sake of another's life, is there somehow something righteous in this act of love/sacrifice?
I can't really give a straight forward answer beyond that God is merciful and just. He knows the heart and circumstances of all things. If one lies to save a life, to distract and deceive someone and give them false information does God in His mercy understand why a human would do such a thing, especially for a loved one? I'll leave that in your hands to determine.