What about other countries adopting BTC as legal tender? Is there still a possibility? Or is it "game over"?
The possibilities will always exist so long as any country having it under consideration can learn from the mistakes of El Salvador and strategically make plans to ensure that those challenges that faced El Salvador in making their plan for Bitcoin as a legal tender to fail do not recur in your country.
Yes, any country adopting it will still have to face its own challenges, but learning from the challenges of El Salvador first brings the country's chances closer to success.