Here's what happens:
* Sonic and Tails are separated. Sonic manages to escape Eggman's base, but Tails gets captured.
* Tails is left behind. The game ends with Sonic running off into the sunset, leaving Tails imprisoned.
* No clear fate for Tails. There's no indication whether Tails escapes or dies.
Theories and Interpretations:
* Tails is implied to be alive: Many players believe Tails survives because the game never explicitly states he dies.
* Tails' fate is up to the player's imagination: The ending is intentionally ambiguous, forcing players to decide for themselves what happened to Tails.
* The developers' intentions are unclear: There's no official statement from the developers on their intended meaning behind the ending.
The Importance of Context:
It's important to remember that the 8-bit version of Sonic 2 is a very different game from the 16-bit version. The graphics are simpler, the story is less detailed, and the overall tone is more lighthearted.
Conclusion:
The "bad ending" of the 8-bit Sonic 2 isn't a definitive statement that Tails dies. It's a frustratingly ambiguous conclusion that leaves the fate of Tails open to interpretation.