Unable to fill board vacancy

This is a NY HOA. Our by laws requires 5 board members. The by laws do not address what to do when we have no one to fill a vacancy. The term has expired for one board member who does not want to run again. We can not find anyone is our community to run for the board. Since our by laws do not address what to do when we do not have anyone who is willing to run for the board to fill the vacancy, can we continue on as a 4 member board? or can the board request the board member whose term is expiring to stay on the board? What should we do. I don't know the rules for the St of NY I looked at the condominium act of NY but found nothing. We are a corporation. Thank you for helping us out.