I love your solution and I like that there will be no Apocalypse and that Zachariah is Andrew was the cream on top.
That was also nice to bring Castiel in without a looming Acocalype. I would like to see how Sam react when he duscover Deans absence and his own reaction the need for Deamon blood.
Can´t wait hope you update soon I am bloody curious, thanks for the great story and for sharing with us.