If I use Sacrifice on a temporary unit and my opponent reacts with Abandon. Once Abandon resolves, can I cast Sacrifice again before the temporary trigger?

Yes, you can cast Sacrifice again before the Temporary trigger resolves.

Sequence of Events:

1. Trigger: At the start of your Beginning Phase, the Temporary ability on your unit triggers and is placed on the chain. This puts the game into a Closed State.
2. Original Play: You play Sacrifice, killing your Mighty unit as the additional cost.
3. Opponent's Response: Your opponent plays Abandon, targeting your Sacrifice.
   • Chain (bottom to top): [Temporary Trigger] -> [Sacrifice] -> [Abandon]
4. Resolution of Abandon: The chain resolves in LIFO (Last-In, First-Out) order. Abandon resolves first, returning your Sacrifice to your hand.
   • Chain (bottom to top): [Temporary Trigger]
5. Priority Window: Because the Temporary trigger is still on the chain, the game remains in a Closed State. You now have priority and your Sacrifice back in your hand, allowing you to play it again targeting your (now protected/still-present, if applicable) unit or another Mighty unit.
6. New Play: You play Sacrifice again. It is placed on top of the chain.
   • Chain (bottom to top): [Temporary Trigger] -> [Sacrifice]
7. Final Resolution: When all players pass, the chain resolves. Your new Sacrifice resolves first (drawing you cards/channeling a rune), followed by the Temporary trigger, which will attempt to kill your unit (or fail if it is no longer a legal target/has been sacrificed).

According to the Chain Rules and established RiftJudge FAQs (like #9866 and #9457), the chain is not a static block; whenever an item on the chain resolves, players receive a window of priority to add new [Reaction] speed effects as long as items remain on the chain.