Is my presence with my father in the hospital during and after his surgery considered an excuse to miss congregational prayers? And is it permissible for my father to combine prayers? And how should he pray if he is not fully conscious and his mind drifts in and out?

It is permissible to miss congregational prayer to nurse a sick person if no one else is available to nurse them, and this is supported by the action of Ibn Umar, may Allah be pleased with them both. Some scholars hold that one whose heart is attached to the patient – even if someone else is available – is excused from attending congregational prayer.

Jurists permit combining prayers for a sick person who finds it difficult to perform each prayer at its designated time. Maliki and Hanbali schools permit combining Dhuhr and Asr, and Maghrib and Isha due to illness. They base this on narrations from Ibn Abbas, may Allah be pleased with them both, and on what is established concerning the Prophet, peace and blessings be upon him, regarding the woman with irregular bleeding, and because the hardship in illness is greater than that in travel. The Maliki school permits combining prayers by performing them early (taqdim) for someone who fears fainting, while the Hanbali school holds that the sick person has the choice between performing them early or delaying them.

One who loses consciousness due to anesthesia is not required to pray until after regaining consciousness, and they should pray whatever prayers they missed as make-up.