Unfortunately we cannot disclose this yet, since the map is being made and hence subject to change. Of course, most of the characters you mentioned will appear in the next chapter, but whether any of them will be controllable by the player at some point of the map cannot be confirmed yet.
Note that the current pattern with the scenarios has been that in each scenario there are two new controllable heros. Whether we continue to do so with Chapter 4, I cannot disclose at this point. But even if we would continue the pattern, the old characters may also appear later in game as additional heros. But no promise.
Yes, he did swear indeed. However, I can't tell you the answer yet. What happens in the Chapter 4 is a secret until the scenario is released. But I can assure you that we haven't forgotten him.
Well, at least Anub'arak won't appear in the scenario. And the Lich King won't make an appearance in person, because at the time of the campaign he is still imprisoned within the Icecrown Glacier. As an overall guideline, we use the original heros of WarCraft quite little, because they restrict our ability to design the story. We may refer to them or to their known actions in dialogue, but typically we won't use them as active heros or even as NPCs in our maps.