Sure the probably scraped the 2nd expansion (story of diablo 3 not complete). And at this stage we probably wont get it.
But what we will get instead is the small new additions every now and then sure it's not an expansion. Sure as content goes it's just a few new tile sets for Rifts and Grifts.
Also i think once the necromancer pack has been released they will have added more content and features Post RoS then in RoS itself. and they will probably continue to add stuff every few months over the next 5 years. and guess what we have paid for it the cost of the char pack (Likley 10-15 USD)
And as for Diablo 3s first micro transaction outside of china, this opens the window for us to get a store with wings, pets, portraits, banners ect and guess what all they added revenue will bring to diablo more developers for more content.
Who knows we might get a new character pack and a few new monster types and tilesets every year now.
And as far as the continuation of the story they could just release a story pack to tell the rest of the story that was probably scraped with the 2nd expansion. When was the last time you played trough story mode (non-speedrunner)
Don't count diablo as dead yet sure it's samey for the high GRift pushers, but they are just a fraction of the Playerbase