This is posted in the wrong forum (I'll move it) and this question has been asked and answered many times.
You will have up-to thirty days after the licence expire before the server will 'stop working', the NE feature will stop and you will be unable to add any new users to the system even if you are below the licenced user count.
What difference does the server make? It doesn't matter on which server you install Zimbra, you should renew your licence and then just move it to the new server.