Does a deceased father's oath that his daughter not work become void upon his death, or is she obligated to pay expiation for the oath on his behalf, or must she refrain from working?

Your father's oath is dissolved by his death, as long as you did not act upon it during his lifetime. Therefore, there is nothing due from him, and no expiation is required of you if you contravene what he swore by after his death, because his oath ended with his passing.