Destiny 2 has gone dark on 30 September 2019 which will prompt any unaware players to ponder what is wrong. Well, nothing is wrong, Bungie are just deploying Shadowkeep and New Light.
Destiny 2 Shadowkeep and New Light are coming on 1 October 2019 which means a huge patch is imminent for existing players. For that reason, the developers announced there would be a 24-hour period of servers going down so the implementation goes smoothly and the services will resume for everyone on the first day of October.
Meanwhile, PC players will need to be a bit more patient, provided they didn't already do their homework. By homework, we mean redownloaded the entire game. Those who already migrated from Battle.net to Steam have to download the entire game again - the old files can not just be copied in a new folder and work properly.
Those who didn't migrate yet, can still do so after the maintenance concludes. For more information about the move, you can check the official blog post from Bungie.
The maintenance is expected to wrap up on 1 October 2019 at 10:00 AM PDT/ 19:00 CEST / 18:00 BST. Following the maintenance finish, expect to see queues and possibly laggy or unstable servers due to the massive influx of new players as New Light will be a free to play version of Destiny 2.