Sure, sargeras(could be) is in a patch,but the whole expansion is centered on Legion. Deathwing was also just a patch, but the whole expansion was about him. So a Void Lord could be a whole expansion in the future, but he will be killable in the last patch only
Dimensius isn't a void lord as in big evil void lords Sargeras is afraid of. There is lots of Demon Lords too, but not all of them is a KJ or an Archimonde.
Sure, I dont really think there will be another Lich King expac, just an idea wich has been floating around this forums. Have to mention though, Legion made The Lich King with the intent to create and control the scourge. So no, it was purely the Burning Legions doing.
Ally/horde vs Jaina could be faction base expansion.
Most likely is the Army of the Light vs Void Lords. That could be at least two expansions, its in about 30-40 years time(lorewise) and seeing each expansion is like 10 and 10 years, 3-4 more expansions to come at least!^^