Seeking to clarify comments made by PC Gamer magazine, suggesting that users would need a constant internet connection to keep playing singleplayer games, Ubisoft told Ars Technica "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".
"Where exactly you are reconnected in the game may differ from title to title. Settlers 7 reconnects at the exact point where the connection was lost, AC2 reconnects you at the last checkpoint (and not the last auto save, as indicated in the CVG article). There are many checkpoints so you're back to the point where you got disconnected in no time."
Ubisoft also explained that if you experience a temporary drop-out (say, a couple of seconds), the game won't be affected, and that the DRM connection only needs 50kps to function, so even if you're on dial-up, you should be OK.
Does that clarify things? Yes. But just because it's clear, doesn't mean it's OK...
Official explanation of controversial Assassin's Creed 2 DRM [Ars Technica]