I must have played with a friend who was further than I in the campaign at some point because I just recently reached a point in the game where I was asked this question;
Do you wish to skip over the missions you've completed in other play sessions or continue as normal?
I chose to continue, as I can't remember anything I've done with anyone else, its been too long. No problems, except about 5 minutes later I accidentally moved ahead too far, too fast, and skipped some dialogue I actually wanted to hear.
To solve this issue, my plan of action was to end-task to skip the auto-save process, and redo the mission and listen to the dialogue. Upon starting the game up, instead of starting at the beginning of the mission, I started at what I think is the end of all the missions it originally asked if I wanted to skip.
Is there any way to fix this? I'm playing on PC.
Best Answer
There are only certain quests that can be "reset". These quests are only the bosses at the end of the game or a DLC. To reset these quests, just follow the ! mark and start the quest like any other.
I found this save editor video if you want to use a save editor to modify your save file. In the description of the save editor video, you'll find these 3 links that will show you how to do this for each of the platforms.
Xbox Save Extraction ►
PS3 Save Extraction►
Gibbed Save editor► http://blog.gib.me/