You haven't said why it is a must? Clearly it is not a must to FD or some backers on here so why do you think it is a must. I'm interested....
it's a must for various reasons:
1 - An offline version is free from any kind of limitations, more fluid, more playable, not depending to the connection limits, etc..
2 - A stand alone game can be sold better (so if crafted some year later from this first online version release it can assure some future to the game)
3 - Final Respect for all those backers of the first kickstarter.
4 - It will stay in the history... (like frontier and elite) an online version can't do this imho.