At the beginning of your upkeep, Celestial Convergence triggers.
In response to the trigger, activate Vampire Hexmage by sacrificing it, removing all counters from Celestial Convergence.
Resolve Celestial Convergence's ability, winning the game due to being the player with the highest life total.
This clever interaction turns Celestial Convergence’s lengthy doom-countdown into an instant win by taking matters into your own hands. As the enchantment's upkeep trigger goes on the stack, you simply respond by activating Vampire Hexmage to sacrifice itself and instantly strip every omen counter away. Because zero counters remain when the trigger resolves, the game immediately checks for the highest life total and awards you the victory.