There is a way to start episode 3 with maximum open paths:
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and all the side plots you go through + Marcus's storyline. See
FAQ (1.3.5).
As for
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- it was never built into the overall plot of the game and is essentially (at the moment) a sort of fanfic from the developer on "what would have been if". This path in episode 2 is quite short, and its passage leads the player to the final credits. In ep3, Revenge Path has only 1 quest sequel so far and it's one of the best quests of the entire 3rd episode and in my opinion, it's worth going through anyway. The easiest way to do it is to start a new game in ep 3 and choose this path - it won't take long.