I am creating an entire campaign in a series of levels with bonus map features, chinematics, voice overs etc. Now, I am about a quarter of the way done but I was hoping to release it after Portal 2 comes out.

I just want to know if you think my progress won't be lost. IE Huge updates to the engine or something.

Well, worst case, you have to redo everything except brushes. Best case, you only have to redo lighting and textures, and go over it to add models and such.

Good news. That's what I was guessing.