They are defenitely developing a standalone client. There’s already been a “leak” on their facebookpage showing a screenshot of the client window 🙂
They also have talked somewhere in the forums or the chat on ga.me about an offline mode.
During the whole development process they are currently not thinking about adding such a feature. But when the game goes live and lots of players are demanding an offline mode they would think about it. (Somewhat like that was written by a dev. If I am wrong – please note it 🙂 )