Well i don’t believe he is dead for 2 reasons. One there is no body. In every tv show you know that if there is no body than there a good chance that person isn’t dead, so until we see a body i say he is alive. The second reason is that I don’t think it realistic that one dagger can manage to kill two people at the exact same time. If it was sword sure I’ll buy it, but a dagger no way. At most he was pierced. I have no idea where rumple is, but he is alive.
Well one thing if for sure: this was his undoing.
But about the dagger: it was magic. That’s why there was the freaky glowy stuff. The dagger cannot pierce both hearts but the dagger of the dark one kills the previous incranation as it makes a new dark one. So the spell bounced back and forth, killing Rumple and his father.
He is most likely powerless now.