Blizzard believes it’s in the best interest of everyone that Diablo III remains an online-only game, and if you don’t have an Internet connection then the game isn’t for you.
Kevin Martens, a lead designer at Blizzard, told Rock, Paper, Shotgun that the people working on Diablo III will not give the game an offline mode, and that’s final.
“If someone has no Internet access, then yeah, Diablo III is not the game for them,” he said.
He also added that Diablo III was, from the beginning, intended to be a game in which players teamed up and interact with each other, and an online requirement was just a piece of the puzzle.
“We didn’t make that game (referring to the offline mode). That’s the straight-up answer. We did not make that game, and we’re not going to turn this game into that game. We have the online mode because we learned a lot over the many, many years that Diablo II was in development.”
Source: Rock Paper Shotgun