The mutation rate is qualitatively higher for languages, and the selection pressure is lower. I think we will all be fine, as concerns maintaining some sort of minimum level of diversity, no matter how things play out, without intervention. The analogy to biological diversity is flawed, because there is no food-chain. We will not topple a tower of interdependent languages if Manx is never spoken again. French and Spanish and Portuguese and Romanian go on just fine without the academicians' Latin.
silly programming language analogy that popped up in a phone conversation:
"...perl is a warehouse full of rope, with a neon sign out front, 'free hanging supplies, help yourself!'. ML says, 'here is a single strand of twine, but I'm watching you!'..."
thoughts floating to the top of my head during the walk back from campus about parametricity of LF functions and commuting with substitutions. Not sure what to make of them, yet.