Does completing the mission "closing the rift" in Dragon Age Inquisition end the main quest of the game?
Solution 1:
No, it doesn't. Don't hesitate to do that missions any time you like, it mostly opens up the game even more.
I'm not far enough in the game myself to verify this, but I've read that the larger part of the main story is still happening after that mission.
The big change after that mission is :
You get your own castle, Skyhold instead of Haven as a base