10 ILCS 5/8-17
If the result of such canvass discloses that such candidate, if he had lived, would have been nominated, such candidate shall be declared nominated.
In the event that a candidate of a party who has been nominated under the provisions of this Article shall die before election (whether death occurs prior to, or on, or after, the date of the primary), decline the nomination, or withdraw the candidate's name from the ballot prior to the general election , the legislative or representative committee of such party for such district shall nominate a candidate of such party to fill such vacancy. However, if there was no candidate for the nomination of the party in the primary, no candidate of that party for that office may be listed on the ballot at the general election. In proceedings to fill the vacancy in nomination, the voting strength of the members of the legislative or representative committee shall be as provided in Section 8-6 or as provided in Section 25-6, as applicable.
10 ILCS 5/8-17