Does undying trigger if the creature was exiled instead of dying?

Undying reads: 'When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner's control with a +1/+1 counter on it.' The word 'dies' has a specific rules meaning in Magic.

Per CR 700.4, a creature 'dies' only when it moves from the battlefield to the graveyard. Exile is a completely separate zone (CR 406), and moving a creature there does not count as dying. Therefore, undying's trigger condition is never met when a creature is exiled instead of destroyed.

This distinction is frequently exploited by cards like Path to Exile or Swords to Plowshares: they exile the target creature, completely bypassing undying (and also indestructible, regeneration, and other death-related abilities).

Concrete example: Your opponent controls a Strangleroot Geist (which has undying). You cast Path to Exile targeting it. The Geist is exiled — it does not go to the graveyard, so undying never triggers, and the Geist does not return to the battlefield with a +1/+1 counter.

The relevant rules are CR 700.4 (definition of 'dies'), CR 702.92 (undying), and CR 406 (the exile zone). Always check the zone the card moves to — only graveyard counts as dying.