I didn't know Emhyr can die in Witcher 3. How? .
None. If CDPR ever make another witcher game and use a single ending as canonical, it would be hugely unsatisfactory for great many people.
The poison chalice that is multiple choice endings. It's bit Bioware firmly in the arse, it'll come back to haunt CDPR if they make a TW4. Sometimes choice isn't a good thing.
Well I've got a hard job, too. Choice is good and Developers should try to meet that challenge instead of making stuff canon.
They rode off towards the sunset. Behind them they left a darkening valley. Behind them was a lake, an enchanted lake, a lake blue and smooth as a polished sapphire. Behind them were left the boulders littering the shore. And pine trees on the slope.
That was left behind them.
And everything else was in front of them.
Whatever the writers feel should be if they want to continue the franchise.