I wasn't too invested in all the "new" Originals, so I will not mind seeing them gone for awhile. Although I will miss Elijah.

Klaus is a hybrid. They've actually explained before why the dagger doesn't work on him way back in season two. It seems like a freaking lifetime ago now.

I don't think Rebekah's permanently dead. It looked to me like Klaus just restaked her with the dagger. His father burst into flames when he was staked with that stake from the original ash tree. And I think the stake got destroyed with him. I could be wrong though.