I'm not sure if this is relevant to the discussion, or if I've come in on the wrong end of it, but ...
Latin is a dead language. I've never heard that disputed.
However there are still latin classes and there are still people who have learned to speak latin very well, and to add new words and phrasings to the dead latin language.
And I think that at least one religion - Catholic, as far as I know - speaks sermons in the latin tongue (I'm not Catholic, so am basing this on an understanding that could be wrong)
And I used to have an english/latin,latin/english transation dictionary, and was devastated when it was lost in one of my moves. It was one of my little cherished books that I have missed greatly. (but I digress

)
So having classes that teach a language, and some people who learn from those classes how to speak the language quite or very well, and others who know lots of words and phrases from that language and can make adaptations to bring elements of the language 'up to date' or add new words, obviously doesn't all add tgether to 'undead' a language.
If it did, latin would not be dead.
So is the argument here around whether a language is 'dead' or 'not dead' -in which case it would appear, using latin as an example, that it would require a population using the language as their native tongue, using it in everyday speech as their primary communication with other native speakers, to make it 'not dead', because learned usage is obviously not enough of a criterian to 'undead' it.
Or is the argument that a dead language can be resurrected for use in some way - like latin, which is to all scholarly definitions 'dead', but has been conveniently resurrected for use in biology, Catholic sermons and for other learned reasons and reasonings?
And if the argument is that a language can be resurrected, but still dead, then that's a different matter, isn't it? Because something that stopped being a native tongue, and was effectively 'dead', could of course be resurrected if a group of people or populace was determined to make sure the language stayed in existence. And the way to do this would be by teaching it in certain courses or schools etc as a specialist subject. It's 'dead', because it's not a native tongue and not in general and everyday usage by a population, but it's been resurrected either for a convenience (latin again) or to make sure that future generations remember the language of their past.
So aren't you all sort of right? - Perhaps it was the phrasing of the question - perhaps one thing was intended in the mind of the questioner, and another thing has been interpreted in the minds of the respondents. So perhaps what you're all saying has correct basis, but just comes from different starting points?
Or am I, as I said at the beginning, coming in at this 'debate' from the wrong end?
If it stayed as a debate, I actually thought it was a very interesting topic tohave been introduced - one that I wouldn have liked to have learned more about
edited to clarify and tidy a bit