What are the common ways to express this kind of sentence:
"It will be possible or not, depending on ..."
"It will be possible or it will not, depending on..."
Are they correct? If not, how can I say it?
You can phrase this as:
< Some factor > will determine if it is possible.
The time we arrive will determine whether we'll be able to get gas or not.
Whether John was able to get the key [or not] will determine if we'll be able to get in tonight.
You can also use dictate in place of determine
Whether they can score in the next 2 minutes will dictate the outcome of the game.