Why was it mentioned in Surat Maryam (And peace be upon him the day he was born and the day he dies and the day he is resurrected alive) that the day of birth is in the past, and the day of death and resurrection are in the future? And does this mean that Yahya (John) peace be upon him had not yet died when the verse was revealed?

The answer addresses the topic of the killing of the Prophet Yahya (John the Baptist), peace be upon him, confirming that many of the early Muslims (Salaf) affirm his killing. It then clarifies the meaning of "peace" mentioned in the verse (And peace be upon him the day he was born and the day he dies and the day he is raised alive), explaining it as an honor from Allah to him during the most significant phases of his life. As for the shift in the Quranic discourse from the past tense (the day he was born) to the present tense (the day he dies), the answer explains that this is a rhetorical device called "iltifat" (transition/shifting) that aims to vividly portray the event and bring it to the listener's mind. It does not indicate that Yahya, peace be upon him, was alive when the verse was revealed, but rather emphasizes that this expression is common in Arabic rhetoric to illustrate the event and its importance.