No, because they asked Kes first.If janeway had to guess that Tuvok and Neelix wanted to murder their own "child" so that they themselves could return to the land of the living and if she did beleive that was their actual wishes and she would comply with those wishes no matter what terminal application that would bring to Tuvix, then by those odds, if Kes wanted her lung back, then somone would have to dig it out of Tuvix's chest and give it back to her.
You do not have the right to take back a gift once it is given. But if you are the victim of theft, you do have the right to your property back, even if giving it back to you would harm the person who received it.
She gave a gift which was stolen. The Giftee fumbled their present putting ownership into contest that the rightful owner of that lung might have reverted to the previous legal and real owner more so than the thief or the semi dead actual owner.
I'm using copyright law as a basis for this crude and poorly made argument.