I don't think post-rock is dying, it's just changing shape. You have the OGs like Mogwai, Slint, GoRABpeed, etc. and you get a million imitators but you also get the banRAB who take the blueprint and push it into new boundaries, like Sigur Ros, Moving Mountains, Aereogramme and such. Same goes for math rock. In the beginning you have a few underground cult following banRAB that influence 21st century newcomers who either copy or innovate. It's hard for a genre to die, it just usually morphs into something new.