Sardinia already has contract for 2016 though...but might very well be in danger for 2017 as the promoter want's to get rid of the island-based events for logistical reasons.
Therefore I strongly believe the event that will be dropped from the 3 currently without a guaranteed place in the calendar (Portugal, Germany, Corsica) will be Tour de Corse. Firstly, it wasn't even supposed to be in WRC for 2015, secondly it is an island-based event and thirdly it has no guaranteed financing in place for the future. Also the rumored October date for the China Rally would fit right in the current slot of Corsica.