"They are coming, so we are leaving."
Translation:Mereka datang, jadi kami pergi.
Honestly, you can use "kita" in this situation. It all depends on the situation. If you are in a group of people, and other people are coming that you don't like, you can tell everyone in your current group that "kita pergi". "Kita" should be accepted because we don't know the context.