Oooh I like that! From what I read around the internet the fight with Strahd can be prettyu easy with the Sunsword. That'll give the players a reason to bother with the Heart of Sorrow

Thanks
I agree with you that him and Rahadin shouldn't be able to wield the sword, being sentient and all. I think it makes sense to hide it in the Werewolf Den, guarded by the werewolves. Another interesting place to take your players!
They should be able to ask a Vistana to throw the cards to tell them where it is.
I don't really have much to add, just reading great ideas to steal for my game