In the latest novel about the Space Wolves called Ragnar Blackmane it is cited that the Flesh Tearers have 100 (?) years to live as a chapter.
However in the Lexicanum it is stated that they will die off in the next 2 millennia if a cure for the Black Rage isn't found. Which is it? Or is this just another oopsie in the W40K continuum? It would be interesting to find out what Mr. Dembski has to say about it.
I will settle for a correct answer about how long the chapter has to "live".