What about the people without Online Service?
Would we not be able to play the last installment of Shenmue? Will we be left in that dark Gulin cave?

I`m hoping Sega puts and offline mode.

probably the most obvious answer to your question is the initial market the game is targeting, which in this case is China and Korea, both of which comprise the largest number of online gamers in the world.

and although recent news has hinted a possible international release at a later date, the main focus is in the above mentioned regions.

Furthermore, Shenmue Online is an Online game, for a totally new market - it's actually based on Shenmue II rather than being an extension to the existing story. Note that it seems to be mainly set in Hong Kong.