They don't need to kill Durance off, the sequel will probably have a new set of companions anyway. Some of our previous ones will maybe make some cameos or get referenced by some NPCs at some point, that's all.
The important thing about companions, though, is that they're expanded. I liked PoE's cast of characters, but I always felt they should've been more reactive to the player's choices and have more content, they had too few interactions with the rest of the world and were too passive outside of their quests. Also, they should add inter-party conflicts (that could result in bloodshed, people leaving and so on) both between companions and between companions and the player depending on what we do. Basically a lot of stuff that BG had and that was missing in PoE. From both Sawyer and Fenstermaker's replies to many post-release interviews it seems they want to add that stuff too, luckily.
Anyway, I think the Vailian republics are an interesting setting, that could allow the developers to go in more unusual directions, as Infinitron has already said. More strange animancy, less classic fantasy locations and monsters.
I hope the sequel will let us continue our MC's adventure, btw. Maybe level 16 is a bit too high for the start of a new game, considering that we've already defeated dragons, archwizards, Thaos, the henchmen of a god and many other powerful entities, but I wouldn't like to start at level 1 again in the sequel (and I think Josh and the rest of Obsidian have said they don't want that as well).