When an associate leaves your orgaization, his/her position remains open until you fill it or close it. As a general rule, you should leave a position open if you intend to fill it within the next six months. Open positions are your way of letting the company know what to project for headcount, so you should review open positions monthly through the lens of whether you still envision filling those seats. Carefully consider as well that in closing a position, you will no longer have access to the history of that position (date created, previous incumbents, period of vacancy, etc.).
Watch the Position Management video to learn more.