I don't remember anybody really making use of six possible endings for each mission combined with the campaign description.ext. The opportunity for betrayal at the start of the Resistance campaign is unusual, but even that doesn't explore the potential.
There is, for OFP, Sam Samson's "It Doesn't Take a Hero" campaign which is only three missions long, but there are seven possible missions to play. (I'm not promising that the following is true for that campaign). If each mission has two possible endings, you can see the geometric progression:
First mission ---> Two possible missions ---> Four possible missions
Considering the workload, you'd have to have a good reason to include a campaign tree for both sides. Most people would say make two campaigns: first for Side A, then Side B; since each can be finished in half the time. The two would have minimal overlap in resources, apart from the intro, since voice-overs for Side A are not going to be heard by a player on Side B.