If a defy gets abandoned, can you replay the same defy after Abandon resolves?

Yes, you can. According to RiftJudge FAQ #9457, it is possible to play the same Defy again after Abandon resolves.

This is because the chain is a sequence of items that resolve one by one, rather than a single immutable block. When an effect (like Abandon) resolves and returns your card to your hand, the chain remains active (assuming other items are still on it), and you receive a new priority window to play reactions.

Sequence of Events:

1. Initial State: Your opponent plays a spell (Spell A).
2. Your Response: You play Defy targeting Spell A.
   • Chain (bottom to top): [Spell A] -> [Defy]
3. Opponent's Response: Your opponent plays Abandon targeting your Defy.
   • Chain (bottom to top): [Spell A] -> [Defy] -> [Abandon]
4. Resolution of Abandon: Abandon resolves first (LIFO - Last-In, First-Out). It returns your Defy to your hand.
   • Chain (bottom to top): [Spell A]
5. Priority Window: Because Spell A is still on the chain, the game enters a priority window. Since you now have Defy back in your hand, you may play it again to target Spell A.
   • Chain (bottom to top): [Spell A] -> [Defy]
6. Final Resolution: Your new Defy resolves and counters Spell A.

This is allowed because Defy is a [Reaction] spell, which can be played whenever you have priority, including during the priority windows that open up while a chain is still resolving.