Hmm... Now, that is an interesting question. I want to say no, but that doesn't mean someone can't have that goal - this is a magical world, the rules change all the time. I'll say it is possible to end a deity's power but not kill them, but don't hold me to it. It wouldnt be very far fetched to have a character with a grudge against a deity.
Just keep in mind I haven't actually posted the deities yet.