I can't see any reason the napoleon tag would ever be relevant on this site, most questions related to Napoleon would most likely be better fit on History.SE anyway.
I think it's safe and uncontroversial to remove tags that are used by a single closed off-topic question. Often this is an indication that questions about such a tag are off-topic.
My only reason for not doing so is that it would bump the question to the frontpage, which isn't all that useful. In this case, just deleting the question would be a better option – this would also remove the tag. I actually cast a delete vote on this question last week when I was cleaning up some off-topic tags and I see someone else added a second vote today, so if one or two more votes are added the question and tag will be removed.