[...] or if the intention is to keep it visible for 6-12 months and then delete it.
Probably that, although I doubt they got a timeline for that yet. But it's kinda inevitable, once it's no longer in active use it'll eventually be seen as dead wood to be cut away.
Personally, I'll see it as a good opportunity to stop procrastinating reading this forum and instead do something more productive. I like Discord for its voice chat quality, but I only intend to engage in that with people I already know well and only on special occasions (like raids). I never got much use out of it otherwise, it usually devolves into idle chatter and memery, which is fine for something like a private guild discord meant for socializing, but I can't see it as a replacement for a discussion board.
Similarly, I like reddit for sharing short video clips, screenshots, fanart and witty one-liners, but especially when a discussion goes back and forth, it just quickly vanishes in the comments as it shifts ever further to the right and leaves long trails of empty space behind. Moreover, I regularly experience issues with copy&paste.