A: The Keyholder is not the only person who can take action to end the round. Remember that in the four player game, nobody knows who the Keyholder is, and the Wizard might be Evil or Good, only the Wizard knows their own alignment.

In the case of an Evil Wizard, here are the possible ending scenarios:
• (Evil) Wizard calls stop, correctly identifying the Keyholder out of three unknowns: Evil wins.
• (Evil) Wizard calls stop, incorrectly identifying the Keyholder out of three unknowns: Good wins.
• Guard calls stop, correctly identifying the Traitor out of two unknowns: Good wins.
• Guard calls stop, incorrectly identifying the Traitor out of two unknowns: Evil wins.
• Keyholder calls stop. In a scenario with an Evil Wizard, the Keyholder can only be incorrect, and Evil wins.
(Of course, it’s a 50/50 chance that the Wizard is Good, so in the opposite case, the Keyholder has an advantage. It balances out.
• The Traitor cannot call stop.

As you can see, it’s hardly impossible for the Keyholder to be on the winning team just because the Wizard happens to be Evil that round.

To round out the win/lose possibilities, of course, there are other outcomes if the Wizard is good:
• (Good) Wizard calls stop, correctly identifying the Traitor out of three unknowns: Good wins.
• (Good) Wizard calls stop, incorrectly identifying the Traitor out of three unknowns: Evil wins.
• Keyholder calls stop. In a scenario with a Good Wizard, the Keyholder can only be correct, and Good wins.

From the Keyholder’s perspective, of course, not knowing the alignment of the Wizard, they have a one in two chance, which is similar to the Guard.