I consider this a normal effect of evolution. Language is a means of communication. In the case of the three remaining "Mati Ke" speakers:
"
...traditional culture has forbidden him from speaking to [his sister] since puberty"
This language definitely does not serve as a communication means anymore, does it? It dies out due to natural selection.
Think of the Inuit: They have 200 (?) words for snow, depending on temperature, flake size, consistency a.s.o.
What if one day the polar ice caps melt away? Will this destroy their language?
If so: this would just be normal evolution, since you don't need 200 different words for something that does not exist anymore...
One should fight the loss of languages, if this loss is caused by pure laziness.
But languages like Mati Ke or the
Gomera whistling language will sooner or later die out, because their initiates die out.
[blue]An eye for an eye only ends up making the whole world blind. - "Mahatma" Mohandas K. Gandhi[/blue]