If you hold your short option position through expiration, you are subject to being assigned to that position. If the option expires in-the-money then it is likely it will be assigned, but there is a small chance that it may not be assigned. You will know before the open the next business day whether you were assigned or not.

If the option expires out-of-the-money then it is likely it will not be exercised. Similarly though, there is a small chance it may be assigned. You will know before the open the next business day whether you were assigned or not. The only way to guarantee that you will not be assigned to the short position is to close out the position prior to the market close.