The Event isn't over yet, but I no longer have the ability to complete Quests

After the Event ends, there is a 24-hour period during which you can spend all your remaining Tokens.

You can't fight bosses or complete new Event Quests during that time! This is your chance to trade in those Tokens for rewards you’ve had your eye on. This is your last opportunity to maximize your gains from the Event.

Remember, once the 24-hour window closes, any leftover Tokens will disappear.