Ars Technica followed up with Ubisoft on the DRM issue (that also affects The Settlers 7), which said, "As long as you do not quit the game, the game will continue to try to reconnect for an unlimited time ... once the game is able to reconnect, you will immediately be returned to your game ... AC2 reconnects you at the last checkpoint ... There are many checkpoints so you're back to the point where you got disconnected in no time."
Ubisoft also assured that the required internet connection speed is supposedly minimal. "Our online services platform will require a maximum of 50kbps of available bandwidth, so even with the slowest connection, gameplay won't be affected," an Ubisoft representative told Ars. That said, it seems that gamers lacking an online connection (or, say, those on a plane or in the armed forces, as Ars points out) may be out of luck if they're hoping to play Assassin's Creed 2 on PC.