Since the dice was an object that Revehecthrax conjured, it would disappear the moment that the Demon exited the battle. There was an item that could make it stay inside the battlefield, but Vernos wouldn't be able to use it by virtue of the restrictions.
The very reason why Vernos wanted to keep the dice was related to its main function. Each side of the dice could change its result every turn. There was a time where he was able to roll a dice and it landed on the side that ended up bringing him victory.
It was the very move that made him win the Meister Clash. That's the reason why many people believed that he won just through sheer luck. What they weren't aware of was that Dice of Fortune and Misfortune could only be acquired by evolving the attack called 'Dice'.
Vernos was hoping that this battle would end up in his favor. No one enters a battle and would wish for their defeat involuntarily.
