The future of HoT
I think that they will continue living story soon after HoT. I don’t think Mordremoth will be defeatable right away when the expansion comes, and living story will continue to build up to a big update where we can kill him. I believe the expansion does come with its own personal story but maybe we only get half of the story at launch? Who knows.
This is just regarding the continuity of the expansion through story though, not sure about fractals replacing dungeons or anything yet.