As the developer confirmed earlier this year, Destiny 2 is going to have a lot of content cut out of it come November 10 to "make room" for the new expansion. In short, they're using the Disney Vault method. Bungie took the time this week to further clarify what that means.
When November 10 hits, a ton of stuff is going to be removed from the game completely until a potential mystery date. While the vast majority of the vault deals with entire areas in the PVE portion of the game (including items and gear), even PVP maps and several modes aren't safe. You can find the full list of content that will be erased from Destiny 2 in November below.
Bungie also says that "With some of the core Year 1 destinations entering the Vault, it’s true that the free-for-all-players Red War, Curse of Osiris, and Warmind campaigns will no longer be playable." They are "building" a new expanded origin story that will launch in Year 4: the quality of which remains to be seen. If you want more info on vaulting as a whole, you can go here.
This whole concept is a mess, and belies the entire idea of Destiny 2 even being remotely close to an "MMO;" a marketing term I dismissed as early as the original beta for the first Destiny. I get that Bungie wanted to reduce the bloat of the game to make it even easier to manage and make the file size more manageable, but it seems like Activision was able to help them out in ways that they can't muster on their own.
Before Bungie transitioned to self-publishing the game felt like one giant world. Now it's been shifted to a monolithic grind framed around "seasons" like every other shooter: with even less content to play come November. I'll be there to at least check out the Beyond Light expansion, but there's less of a reason to linger now.
This Week at Bungie [Bungie.net]