Just a suggestion;
Let it still drop a card but disable the ability of the card. Then make a Reward System for players to exchange the card onto an item/zeny, depending on the rarity of the card. Or maybe make the card a component or requirement for crafting something valuable.
Players always lookup for that moment/experience when an MVP/Mini card drops. And, it's one of the reasons why this game is very fun and exciting all through the years.
Again, just a suggestion ;)