Frozen game and broken build
Solution 1:
Yep...the build is gone, from what you said. If I remember correctly, same happened to moi.
My reason it's lost : Exiting the game requires saving, no matter what (unless you crash or force quit, etc) You saved the world with the chunk not there.
I don't believe you can get it back, but i recommend using mcedit, as that will read the files in the mc folder and hopefully read the "missing" chunks, if it is still there.