How can one pray, fast, and worship in the shadow of nuclear war and its ensuing global famine, nuclear winter, and nuclear summer?

Asking about groundless or improbable assumptions is blameworthy. One should occupy themselves with what is beneficial and strive to do what Allah has commanded, abandoning sophistries and asking about what has not yet occurred. Many Companions and Successors disliked asking about events before they happened, as explained by Al-Hafiz Ibn Rajab, citing the sayings of Umar ibn al-Khattab, Ibn Umar, Zayd ibn Thabit, Masruq, Al-Sha'bi, Tawus, and Mu'adh ibn Jabal.