You'll have to look to the rules of your plan. Generally, though, the account owner retains control of the account if the beneficiary dies. The account owner may be able to name a new beneficiary (which may create gift tax or estate tax consequences). Or the account owner might make a withdrawal from the account. If so, the earnings portion of the withdrawal will be taxable.

Note that if the beneficiary dies with a balance within his or her Section 529 account, the balance may be included in the beneficiary's taxable estate.