That is the risk of outing as a mercenary then. If you out to your contract, you better make damn sure that they will stay alive or you will be outed as what your next faction will be. In the previous patch, you would simply suicide and lose, so why would this win condition be so much harsher? The “new” win condition should be to survive to see the opposing faction (opposing to the mercenary’s target faction upon dying) win. In that way both BD and unseen/cult have ways to get the mercenary on their side. The BD can kill the unseen/cult Mercenary target and get the Mercenary on their side. The unseen/cult can convert the target and keep it alive or kill the BD target. The Mercenary should still lose all their abilities or maybe get a very weak new one. This would make Mercenary a very deep class with shifting allegiances like a true neutral.
I’m just spitballing. I know this idea has its flaws as well, but it eliminates the purely a random extra number for whatever faction at the start of the game flaw.