Larian’s Swen Vincke posted a tweet yesterday showing the game hitting 500,000 concurrent players, making it the third most played game on all of Steam He said that he told IT to only expect 100,000 concurrents at max.
Game is designed to be online by default, even though you don't see it. If you want to play offline you have to go and disable multiplayer. Hence my comment, they shouldn't make something always online if they are not ready for the traffic. If you switch to offline mode some events become unavailable. Although it is praiseworthy that they have enabled it to be played offline.