The issue to me is the extent to which we should mourn this inevitable language loss or simply note it. I can see a good argument for maintaining genetic diversity in biological systems because it is the substrate for adaptive change, for evolution. I'm not sure one can say the same thing about language. I suppose if we ride the language-determines-thought hobby horse a little we could argue language loss correlates with loss of ways of thinking, but I'd want to see real data before I accepted that metaphor as a real thing. If we see language as simply a tool, although a beautiful one, then humans are always devising new tools. And, since it's a communication tool, the more we intermingle the more likely we are to discard old versions of it.