Illinois state law "doesn't cover how to replace Senate candidate dropouts," the Daily Herald reports. "The buzz among Republican insiders is several party leaders have spoken to U.S. Senate nominee Jack Ryan and asked him to get his divorce file situation straightened out sooner rather than later."
If the documents about Ryan's divorce settlement "are released and the information proves fatal to Ryan's campaign, election law makes no specific provision for who appoints a new Republican U.S. Senate candidate." (See the AP for more on Ryan's effort to block the documents.)
"The odds are the state central committee would get to pick a successor, but given the unpredictability and split among the state's GOP, a lawsuit could be filed to block that."
Update: Rick Hasen notes the article "does not mention one of the trickiest issues related to this question."