*Appears from a dark ally*
Psst! Hey, you there! There is actually one thing you can do...
1) Create a story arc where the final mission has a success and fail condition, plus differing contact messages for each outcome
2) Within the 'success' message, tell the player the registration number of the story arc for proceeding on the success branch of the story
3) Within the 'fail' message, tell the player the arc registration number that continues the fail branch
For multiple branches, maybe just add global alts to give you more story arcs to publish.
If you make each AE story quite long, it will take the player a while to discover all the arcs you've created, representing the branching paths. 🙂
For bonus points, make the fail conditions in the branching missions/arcs a matter of player choice, empowering them so it feels more like they can choose between X vs Y instead of succeed vs fail. e.g. "Escort the hero to the exit, OR deliberately walk them into a mob of enemies and gett them killed, just like your contact or a different NPC suggested earlier..."