I agree with creating a 'series of the season' subforum under General Anime, templating the titles of each thread something like Code Geass: Episode 01, and throwing it all into another 'death of series of the season' subforum when GW moves on to another highly loved anime. It will sort of stave off of losing discussions from simply deleting or invisiblizing forums, keep the confusion out of merging 26 forums together for later readers, and still allow some separate discussions about issues that arise from each episode to continue.

In my opinion the forum should still have posting permissions, because though the posting volume will most likely be decreased in specific threads, people still might want to debate on things like 'who's leg was whose' in that shot, and the ultra specific philosophical crazy stuff they like to debate per episode.