1. If serana just up and cured herself of Vamprism from the second she learned her blood was needed to fulfill the Tyranny of the Sun prophercy Harkon would never have even been able to block the sun out because her blood would become that of a mortal and therfor useless, only Serana's mothers blood would then suffice but she was in the soul cairn with no way of Harkon ever getting to her.
2. why do you have to bring the bow with you to castle volkihar if you are with the dawnguard? you don't need the Bow to kill him, just say if Harkon managed to kill you that would have been the biggest mistake the dawnguard would ever had made, best bet would have been to keep it locked away in fort dawnguard instead of foolishly bringing it with you.
For me, since I like to play the vampire side:
1. Curing vampires is a myth. There's only one cure -- kill em. Plus she is a worshiper of Malag Bal, so curing makes no sense. Some of her dialog points to this. As for leaving Valerica in the soul cairn, what a waste of a royal vampire. I always free her.
2. Its the only way to prove to Harkon that you are stronger than he is.[/quote
No you can remove the Gift of Vampirism by Going to Morthol to see Falion but I don't see why any would as Theoretically Vampirism makes you Immortal while the lesser conditons do not but if you cured Serana when she learned that her blood was needed then her blood would not work also why does she fight harkon with you for knowing that you also brought Aureil's bow with you put 2 and 2 together and the sun would be permantely blocked out which really I don't see why it would have been a problem about the mortals attacking them and whiping out there kind as for 1 the mortals would never find out as it is obvious that when you block out the sun that even the smartest have no idear whats happening so therefor theMortals attacking them should have been the least of their worries the vampires would have had this chain reaction happen.
1. The sun gets permantly blocked out the Vampires are happy
2. Plants start to die for lack of sunlight
3. Animals who eat plants start dying out
4. People who rely on Animals and Cropswill Starve and Eventually Die
5. Mortals numbers get Scarse
6. Vampires are all that's left
7. No Blood so they all get mad and regret blocking out the sun unless they want to start draining eachother
(and if that happened eventually there would be one vampire left to wallow in Misery forever)