Edited Peter Davies (July 24, 2018 11:13:39 PM)
Three types of triggered abilities do not expire and resolve immediately if they are discovered:Most likely, Nancy will choose to resolve the default action, and Alex loses the game immediately.
• A triggered ability that specifies a default action associated with a choice made by the controller (usually “If you don't …” or “… unless”). The opponent may choose not to resolve this trigger. Otherwise the default action must be chosen.
A player controlling another player is responsible for that player’s triggers in addition to their own.So, Alex is responsible for Nancy’s Pact trigger, and can simply choose not to pay for it - Nancy would lose the game, at that point.