Nope. You can play without buying RotW. You may need to login with the Battle.net client and update your installation to make sure that you have the latest version.
I had this issue. The only thing that worked for me was to uninstall and reinstall from scratch.
Thank you. I did and I manage to log in after re-installing the game. However, the entire game is bugged on character screen. I could only press play or lobby. Pressing play leads me to select a normal, nightmare or hell game. And when I am in, the screen just keeps flickering at camp.