Although Destiny is going to have a campaign that can be approached by the solo player, Bungie's Jason Jones has confirmed that there is going to be a point where players will need to approach content in groups, or they'll run the risk of not being able to progress.
In a recent interview with Game Informer, Jones revealed how the single-player campaign would morph into something that requires co-operation between players.
"You absolutely are going to be able to play Destiny by yourself and have the same kind of fun shooter-experience that you could have in a single-player campaign, which is a word that we've weeded out of our vocabulary, but we're going to give you this great player-progression on top of that, and we're going to give you as many opportunities as we possibly can to expose you to other people, so that hopefully you're drawn into some social experiences, because those are incredibly powerful and interesting, but we're not going to force those on you."
Jones continued: "We describe it in a lot of ways as sloping the floor towards socialization, without putting a requirement on it. I would say that there's some sort of - if you wanted to talk about it in MMO terms, you'd say "end-game activities", but some of the most intense non-competitive activities in the game do require cooperation. They require a group of players to tackle at once. I guess at some variable, distant endpoint we are going to say, "Yeah, if you show up at this door, and you don't have five friends, you're not going to be able to succeed," but the core experience that solo players have enjoyed in shooters, they're going to be able to get that, and we're going to pull many of them into social experiences as well."
Destiny is going into beta next summer (first on PlayStation platforms), before being released on Xbox One, PS4, Xbox 360 and PS3 on September 9.