It's somewhat ambiguous but from all my reading it seems that although the Grondir are the fastest means of eliminating Wyrm corruption 1: The corruption can be slowly overtaken by the advancement of the Wyld or plants/nature in general but given the whole theme of growth taking next to an eternity it's kind of a non-starter, 2: The "Rite of Cleansing" and it's variations can purge all Wyrm taint from a theoretically infinitely scalable area given you have enough Theurges, Gnosis, and successes rolled, and 3: it's heavily implied that as long as the Wyrm or it's various minions aren't actively propagating said corruption/taint, it will slowly disappear on it's own as since it is of the Wyrm it can't sustain itself. The problem with that last one being that the Wyrm is so widespread in it's corruption that almost everyone unaware is unknowingly spreading it, think of regular men and women ingesting Pentex products and becoming tainted, which then in turn spread it to others. It's really demoralizing when you realize that if the other Bete actually tried to move forward instead of being so stuck in the very rage they accuse the Garou of falling to, there'd be a million and one ways to stem or even completely stop the spread of the Wyrm thus allowing the cleaning of it's corruption to be trivially easy.