This is a no-brainer! If it is not legal, it's not ethical either! Let it walk!
A few years back I could have shot a trophy buck, but I did not have a tag for it. I could have had a buddy tag it for me later, and I probably could have gotten away with it too. At the time I had shot only smaller bucks and does, but the thought of having an illegal trophy on my wall as my first trophy deer was more guilt than it would have been worth! I would have been ashamed of myself to this day had I shot that buck! Passing up an illegal deer is part of what separates a true hunter from a killer! Killer isn't the word for it, I think the word is POACHING!