Must a wife fast a month as a form of self-discipline—considering her vow is a miser's vow—even if the condition of her vow, namely her husband's reform, has not been met, given that she vowed to fast a month if Allah reformed her husband and he became a scholar?

The general ruling on vows (nadhr) is that they are disliked, due to the Prophet's (peace be upon him) saying: "Indeed, it does not avert anything, but rather it is used to extract [wealth] from the stingy." And his saying: "A vow does not bring forth anything for the son of Adam that I have not already decreed." Despite being disliked, a vow of obedience must be fulfilled, based on the Prophet's (peace be upon him) saying: "Whoever vows to obey Allah, let him obey Him; and whoever vows to disobey Him, let him not disobey Him."

Therefore, your statement: "If Allah reforms my husband and he becomes a scholar, I will fast for a month," is a vow of obedience contingent upon a condition. If the condition is met, then fulfilling it becomes obligatory. If the condition is not met, then nothing is incumbent upon you, as jurists have agreed on the permissibility of making a vow contingent upon a condition, and that fulfillment is not obligatory except after the fulfillment of the condition. Better than making a vow is to advise your husband, help him, and pray for him.