You can play through the campaign, save and load. None of the unlocks are saved (aside from which missions you've unlocked). The campaign is very short however and designed with you replaying missions multiple times using unlocks, different entry points, and start disguises (all of which have to be unlocked in online mode for them to become available offline). Also, there isn't any other than the "singleplayer" aspect to this game. All that online mode does is tracks your progress and unlocks stuff (you really are suppose to replay these levels multiple times in many different ways, which is why people are so annoyed by online requirements still being there) and puts you on global leaderboards (which have top results filled with cheaters anyway).