Sadly what Sertorius said is true, or thought to be anyways. Tetricus planned to lose the battle from the outset to save himself, if you want a surviving Gallic Empire, your best bet is for Postumus to survive longer and have a hier to take over.
And even then, it wouldn’t survive long, the Gallic Empire wasn’t born out of any cultural or political dissension, it came to be because the Western provinces lost confidence in the central authority’s ability to protect them from the onslaught of foreign invaders. Even if Postumus had survived the attempt against him, Aurelianus would have fought against him regardless, and unless Postumus killed him, or at least defeated him in a crushing victory, the Gallic Empire would have been rapidly dissolved and the provinces restored to Rome.
And even if Postumus had killed Aurelianus, he’d have just bought some more time for himself, Probus would have taken the Gallic Empire back, likely after Postumus had been muredered.