Hunch. On 2 October the party's Vaud branch said it hopes French-speaking party members can keep the seat Guy Parmelin won in 2015.
The French speaker market resolves on the party's press release on its list: YES if the list adopted on 20 November names at least one person from French-speaking Switzerland, such as Céline Amaudruz or Pierre Alain Schnegg. If the decision moves, the market follows it until 8 December, with no list by 9 December it is VOID, and swissinfo and RFI are the backups.
We looked for cases where a minister from the Social Democrats on the left or the Swiss People's Party on the right left the government in the middle of a term, and parliament filled only that one seat that day. We found five such elections since the seats were first shared out in 1959. Each time the party of the minister who left kept the seat. (Swiss Parliament; Swiss Parliament; swissinfo; RFI)