I agree that if a language is dying then it should not be saved to perpetuate its use. If the language is dying then it has essentially shown itself to be an inadequate means of expression for the modern world and that it is unable to adapt itself to express new ideas.

That said, I do believe that languages ought to be preserved for academic study since every language is a reflection of its culture and expresses ideas and concepts that are not easily expressed in other languages. For instance, you'll find in a language like Arabic, spoken by desert dwellers and nomads, figures of speech, proverbs, and other expressions depicting the importance of water which would not be found, for instance, in languages spoken by populations in lush, agricultural societies. Something similar could be said regarding regions that experience an abundance of water like South East Asia which has the monsoon season. Although the preceding example is mundane, what I'm getting at is that letting a language disappear is depriving oneself of novel modes of thought and expression.

I think every language has rich concepts to offer other languages. If we don't preserve the languages we do have, we may very well be shielding ourselves from potentially revolutionary ideas.