The Patch 7.3 will be the last major content patch for World of Warcraft: Legion. However, this does not mean that the story will be concluded. Game Director Ion Hazzikostas discussed the current status of the story in an interview at gamescom.
Hazzikostas says about 7.3: “It is the last major patch, yes. When it comes to large, open zones to explore, raid tiers, dungeons, and such. But it is not the end of the story of Legion.”
Even though 7.3 is the last major patch of WoW: Legion, Hazzikostas emphasizes that large content patches are not the only way to tell stories. There are now smaller and larger ways to continue the story. New techniques allow for this.
Hazzikostas gives as an example the 10-week campaign that led to the opening of the Night Fortress. Or the moment when Harbingers filled the streets of Dalaran. Or the moment when Argus suddenly appeared in the sky over Azeroth.

At Blizzard, they appreciate having different ways to bring game content to WoW. Ideally, this should prevent content droughts.
We have already provided a small preview of the loot from Argus here, with two nice tank trinkets