The correct way to say goodbye to a friend not seen for a long time is "¡Adiós!".
When saying goodbye to a friend whom you might not see for a long time, the correct option is ¡Adiós!. This term is commonly used to bid farewell for a longer duration. Other options like Hasta luego (See you later) or Hasta mañana (See you tomorrow) imply a shorter time frame.
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