Yes. From what I hear you will have access to any DLC content while you are subbed. If you drop your sub you will lose access to the DLC and be required to either re-sub or purchase it with crowns.
ZoS_GinaBruno wrote:
Anyone who owns ESOTU and has an active ESO Plus membership will also automatically have access to the Imperial City DLC game pack. If your ESO Plus membership ends or lapses, you will no longer have access to the Imperial City DLC game pack content and areas, but you will still have any items you earned while you had access. If you do not have an active ESO Plus membership you can purchase the DLC game pack for 2,500 crowns via the in-game Crown Store.