"4)(a) In the event that death, resignation, withdrawal, removal, or any other cause or event should cause a party to have a vacancy in nomination which leaves no candidate for an office from such party, the Department of State shall notify the chair of the appropriate state, district, or county political party executive committee of such party; and, within 5 days, the chair shall call a meeting of his or her executive committee to consider designation of a nominee to fill the vacancy."
Whomever the executive committee names is the nominee running under Foley's name. Of course, I am not sure there is such an executive committee for a multi county congressional district. That may be a lacunae in the law.