DDoS attack on Blizzard leads to more calls for a Diablo 4 offline mode | Some players were unable to access the game for over 12 hours
On Sunday morning, Blizzard tweeted that it was actively monitoring an ongoing DDoS attack that was affecting latency and connections to its games.
There's no reason for them to withhold an offline mode from users.
Edit: Oh, shit. I can't believe I forgot about greed.