Is there any way to react to a Glasc Mixologist getting killed by sacrifice?

Yes, you can react to a Glasc Mixologist being killed by a sacrifice effect.

According to Rule 428.1.a.1.b, when a unit with a Deathknell ability is killed due to a kill instruction (such as a sacrifice effect), its Deathknell is added to the chain as a pending item before the unit is moved to the trash.

How the Interaction Works:

1. Kill Instruction: When the sacrifice effect (the "kill instruction") is played/activated, the Glasc Mixologist is designated as the target.
2. Deathknell Triggers: Before the Glasc Mixologist is actually moved to the trash, its Deathknell ability triggers and enters the chain as a pending item.
3. Chain State: Because an item has been placed on the chain, the game state becomes CLOSED.
4. Reaction Opportunity: Once the Deathknell ability is on the chain, players have the opportunity to play [Reaction] cards or activate [Reaction] abilities.
5. Resolution: Once all reactions are resolved, the chain resolves (LIFO). The Deathknell ability will resolve, allowing the controller of the Glasc Mixologist to play a unit from their trash.

Important Considerations:

• Targeting: If you are the opponent trying to prevent the Glasc Mixologist from successfully playing a unit, you can react to the Deathknell trigger on the chain (for example, by using a card that targets the trash or interferes with the playing of the unit).
• Rule Reference: Per Rule 428.1.a.1.b, the game notes the information of the unit (such as its location) to process the Deathknell before the kill instruction finishes executing, ensuring the Deathknell trigger is successfully placed on the chain.

This interaction is consistent with how Deathknell abilities handle pending items on the chain, as established in the Riftbound Unleashed rules update and supported by several RiftJudge FAQs (e.g., FAQ #9783, FAQ #9149).