You can if you have the evidence of him/her leaving the game (if they haven't logged in for awhile it is a good indicator) if you pass all information relevant onto the help desk and tell them about the situation they should allocate CEO to someone else, I don't know how the "selection" process of the new ceo works, it might just be the person sending the ticket in.

http://support.plarium.com/ensoldiers/Tickets/Submit/Step1/51

I believe there is a minimum requirement for how long the CEO has been out of the game though (I think it is 1-2 weeks) or any evidence that would suggest he/she left entirely... For example messages.