http://wbcboxing.com/downloads/WBC_Rules_&;_Regulations_amended_as_of_November_2015.pdf
＞(b)　In a title bout, if the challenger wins and is later found to have violated these
＞anti doping guidelines, the WBC may declare the title vacant. The WBC may
＞then order any bout(s) or take such other action to fill the vacant title
＞as it may determine in its sole discretion

空位になってその後は決定戦で決めるか他の手段で決めるか結局WBCの裁量次第