When your ZCS Network Edition License expires, a license expiration warning will appear in the administrative console and web interface for all users. From the date of the license expiration, there is a 30-day grace period during which the warning message is displayed, but no features are disabled.
Upon expiration of the grace period, the server will revert to the feature set of the Open Source Edition. The following is a list of some of the major functions that will no longer be available:
If you do not plan on renewing your license, you can again regain the ability to create/delete accounts by "upgrading" to ZCS FOSS. You should choose the same version of FOSS as you are currently running on Network Edition for this transition, after which you can upgrade to the latest version of ZCS FOSS.