If Koster loses or Missouri senate vacancies don't work that way, forget it.
Governor appoints someone to serve the rest of the term.
If there is someone who has a better shot than McCaskill at winning in 2018 and Koster wins, I'd say there is a strong argument in her moving on up so the better candidate can weather that storm.
Regarding what Sanchez said, the point of avoiding incumbents is that you risk your majority for a position one easily could have filled with someone else. In this case, there is no risk if Koster wins. He appoints a (hopefully) stronger replacement who still has the benefits of incumbency 2 years later.
I wouldn't put it beyond Hillary. After all, she picked Kaine for no
good reason and effectively put a Senate seat in play for the next 2 years, once during an off-year low turnout election and next in a midterm that was already looking ugly for her party.
