In some ways, if you can see an inheritor of post-punk's confidence in speaking out and shouting down power and the effectiveness of words, it's heavy metal. Which is not genealogically or genre-ologically part of the punk/post-punk/alt-rock lineage at all.
Maybe a few genes have drifted over from Goth or industrial, but historically there's really hardly any link. As was mentioned before, metal was the enemy, as far as post-punkers were concerned.
But now, through its own evolution through thrash and death and black metal, it's reached a place where much of what characterised post-punk - the darkness, the dread, the wordiness - can be found in its vital contemporary form only in the metal underground.
You'll also find there that whole set of ideals to do with musical progression and fusing different styles together. Extreme metal is totally committed to ideas on innovation and genre-splicing
Interesting in light of yesterday's reflections on the NME's top 500 albums of all time. Is modern day indie is so locked into resurrecting the the past that - individual auteurs aside - the innovators, those holding up a mirror to modern life have largely moved on, whether that's metal, hip hop, electronic music or elsewhere?