Does an oath take effect and necessitate expiation if a person says "By Allah" then qualifies it with "if Allah wills" after repenting from sins, but does not complete the sentence stating that he will not commit them again?

Whoever makes an exception in his oath immediately following it without a break, the exception benefits him, and he does not commit perjury. However, if he makes an exception after the oath and there is a separation between them, the exception does not benefit him according to the majority of scholars. If you did not utter the matter sworn upon, then your oath is not binding. Using oaths to compel oneself to abandon sins is an unsound approach. The straight path to abandoning sins is to seek Allah's help, be conscious of His greatness, and offer sincere repentance.