Here's why so many languages die: There are not enough linguists in the world to record languages. One of my professors working with a nearby tribe on language revitalization. After like ten years of research, she has a decent grammar (rules for articulating sounds, interpreting the sound system, making words, making sentences and interpreting sentences) and a medium-level dictionary. 10 years and she still doesn't have definitive resources.
Also, the whole claim about creating an orthography for language being impossible is moot. We linguists can capture subtleties in language. For instance, Rebecca's claim that these languages are verbal (she's probably thinking primitive) is true for many polysynthetic languages. In these languages the domain of a sentence can be a single word.
Here's an example from Wikipedia:
Aliikusersuillammassuaanerartassagaluarpaalli.
aliiku-sersu-i-llammas-sua-a-nerar-ta-ssa-galuar-paal-li
entertainment-provide-SEMITRANS-one.good.at-COP-say.that-REP-FUT-sure.but-3.PL.SUBJ/3SG.OBJ-but
'However, they will say that he is a great entertainer, but ...'
Here we see the nuance you guys were talking about. The second line shows all the atomic units of meaning of the molecular sentence. Beads on a string. Polysynthetic grammars can be exceedingly precise and all the subtleties have a surface representation.