What are the consequences of not fulfilling a vow to write a book on scientific miracles in agriculture, and is expiation (kaffarah) obligatory, and if so, what is it?

A Muslim must fulfill his vow as much as he is able, for Allah has commanded fulfillment and praised the righteous for it. A vow revolves between what is permissible (mubah) and an act of worship (qurbah). Scholars have differed regarding vows concerning permissible matters. The Hanbalis believe that one is given a choice between performing the action or offering an expiation for a broken oath (kaffarat yamin), while others believe that such a vow is not binding and entails nothing. Writing a book on the scientific miracles in agriculture and demonstrating Allah's power in plants is considered, in this era, a binding act of worship, and it may even reach the level of a collective obligation (fard al-kifayah). If you are unable to write it due to an inability that is unlikely to cease, then you must offer an expiation for a broken oath, based on the Prophet's (peace be upon him) saying: "Whoever makes a vow that he cannot fulfill, its expiation is the expiation for a broken oath."