For single player lovers who are looking forward to Marvels Avengers but are worried it might get caught in multiplayer trappings, take heart. The game is very much going to have a co-op side to it, but weve already been told by the developers that nearly everything in the game can be played solo. In fact, you dont even have to be online if you want to play the game.
Source: N4G PC Marvels Avengers Has A Huge Spine of Single Player Cinematic-Led Story; Can Be Played Offline