There's no way you can prepare very well for that kind of scenario. I would figure that IF I could get through safely, I would probably be talking about ten days, minimum.
I think one of the worst things about this kind of situation would be the fears of the people 'back home'.
You would know that you were (relatively) safe, and working your way back. They would not only be busy trying to survive, but would have the extra stress of not knowing how you were doing, or where you were.
I can't think of any kind of communication that would be guaranteed to work in this situation.
I guess I would try a little of everything, and hope I could get word to them that I was heading home.