What Are the Long-Term Consequences for the Attacked Coin’s Value?

The long-term consequences are usually catastrophic. A successful 51% attack destroys market confidence, as the coin is proven to be fundamentally insecure and unreliable.

This leads to a massive and often irreversible price crash, exchanges delisting the coin, and the community abandoning the project. The coin may effectively become worthless, as its core promise of decentralized, immutable transactions is broken.