If the server is just down and you still can log in the game then you ca us editor offline ... if that red window don;t bother you ... i mean you can try ... log in game go in editor then unplug your network connection wire and you see you can still build and save your work ... the only thing is you have to move that red little window with connection lost or something like that
... and yes we never going to have the editor offline since this is a subscribe game