"still up in the air" means that decisions have not yet been made or that plans are not yet finalized.
I'm not sure what we will be doing this Saturday. We'll decide on Friday. Right now, our plans are still up in the air.
Once things are no longer up in the air, they have either "fallen into place" or "fallen apart".
fallen into place = everything worked out.
fallen apart = nothing worked out.
Here's a great idiom website I stumbled upon many months ago. It has definitions and the history of how an expression came to be:
http://www.businessballs.com/clichesorigins.htm