Because Malack doesn't say "it would kill me" at any point. He says it would "Destroy the person he is today." Implying that he would not outright die, but would lose a fundamental part of his person (ie the vampirism).
So youre now suggesting that not only does he have the shaman's memories, he has his personality too? So... besides being composed of negative energy, how is there a possessing spirit in this scenario at all?
unless youre talking about this comic I cant find the scene youre thinking of. And if you are talking about that one, obviously they aren't done there yet. They haven't found the gate at that point.
possibly, but Durkon immediately know that it was the sun burning him, and both he and Malack were able to survive for a little while in the sunlight. Long enough for Durkon to go "Oh crap, sun!" and turn around, at least.
Again, the fact that it could have inspired him doesn't mean that it is a reliable or relevant source for what happens.
That doesn't even make sense. Durkon is, for all intents and purposes, not there for the purposes of conversation. Plus, up to that point, she WAS talking to the dark spirit specifically, since we can see Durkon having no say -at all- about what is happening. he cant even taunt futilely at Hel.