mission expiration

System

how permanent will our missions be? Will they expire if no one plays them after so long? Also, what happens to them, when and if a new version of the foundry is released? I just hope that once a mission is made that a future update won't break them, or have some unwanted consequences. Furthermore, will we be able to take down our missions for revisions to take advantage of newly added features, and then repost them? or will we have to recreate them again from scratch in order to use them?