Anyone care to explain the co-op save system?

[allas]

So I was playing with my friend yesterday and it said only my quest progress will save. We tried to continue playing today and he was unable to join because he wasn't so far in the story. What is the way to play this game correctly in coop so we can come back to it later?

[B0Tzerker]

The player who is further ahead needs to join the game of the player who is further behind. The player further ahead will in a sense be replaying missions while helping the other player to catch up. If both players stop at the same point then it should not matter who joins whos game when you both resume together.

When the player who is further behind joins the game of the player further ahead, he may not get credit for missions completed as his solo game progress has yet to complete required missions.

[allas]

Ok, and what happens when the player that is ahead joins the player that is behind, but they progress further than the first player was originally, does that progress save for the first player? Because if it doesn't won't they just have to play everything twice to progress?

[B0Tzerker]

Yes it will save forward progress and the player who was initially ahead will not have to replay anything.