No matter what they've said, and they haven't even clearly said anywhere that artifact weapons aren't gonna carry over into the next expansion, but even if they had, AP has become too much of a universal reward for them to give it up. It's something they've wanted to do for years. Whatever content you wanna do at max level - dungeons, raids, PvP, quests - you can do it, and get a reward that helps you progress your character over the course of the whole expansion. There is no way they are just gonna let go of that.
I'm gonna copy my other post in here for anyone trying to lecture me on Blizzard having outruled artifact weapons for the next expansion.