I don't know based on the rulebook.

The provided rulebook context does not specify what happens to a Monster's Power cards or Energy cubes when that Monster is eliminated during another player's turn. The rules explain how to buy and use Power cards, and how Energy cubes are spent, but do not address the fate of these components upon elimination. To answer this question, the rulebook would need a section or rule about what to do with a Monster's possessions when they are eliminated.

Source: pages 2–6.

Source: Core Rulebook (pp. 2, 3, 4, 5, 6)