He is not one to let his problems be known. I have 2 children who are very attached to him and he has just like disappeared with no answers nothing. Saying he needs to get his self taken care of first before he can worry about anyone else, after telling my son in the onset of this depression in Feb that he wasn't going anywhere he was just going through a real hard time. Sounds like a very unpleasant situation. I will address your questions as best I can 1.
Episodes can last days to years.
I cannot tell you how long it will last. It is not normal to run away, but it is not uncommon, either. I do not know anything about his coping style and personality, so depending on how he is constituted, the behavior may be part of his illness or just part of his baseline personality. Even if he returns to his previous state, there is no guarantee that you and the children will. There is water under the bridge, and you or they may harbor resentment over the course of events.