What happens when a visitor deletes Cookies?

A visitor is recognized by a unique identifier stored on the visitor's device,  in a cookie. But what happens when the visitor deletes his browsing data and with that also this identifier?

The Site identifier that has been created on the device is no longer available. If the visitor lands directly on the website without passing by an email, a new identifier is set on the device and a new anonymous profile will be built. If the visitor lands on your website by clicking through in a Engage email, the tool will automatically re-identify the visitor and merge his previous identified profile with the new data.

If he was custom identified before, and again logs in on the website, he is also automatically re-identified and his profile data merged.