I thought that was a wonderful end to the fourth season - although I am sad to see Gus go as he is such a great character. I think that in the final season (which is set to be 16 episodes) Walt will get cooking straight away. He might get help from Mike to distribute through Gus' network, or he may start afresh, or he may sell wholesale to someone else. Either way, there is a meth vacuum that needs to be filled.
I love the way they have developed Hank's character - for me he is now the main man and ultimately this show is heading towards a Heisenberg/Hank showdown.
Also, we haven't heard the last of Gus, in terms of the much alluded to connections and protection he has from Chile. That's going to come calling for Walt I reckon.
I read the script for the first episode recently and it is amazing how different it is from the eventual pilot. It's set in California, Hank is a total racist, Walt is a compulsive masturbator.