Here is another way to look at it.
We remember that there are only four paramatta dhamma: Nibbana, rupa, citta, and cetasika. The latter three entities belong to “this world” and Nibbana means dissociation from “this world”.
The easy answer is: Nibbana is detaching from this world. So, all three entities of citta, cetasika, and rupa cease to exist. There is no mind without citta and cetasika. So, when the mind becomes free of asavas, the mind itself cease to exist.
Another way to look at it: The Buddha said that a living being (satva or satta) is the collection of five aggregates: rupa, vedana, sanna, sankhara, vinnana. Furthermore, ALL FIVE must be there together, i.e., mental components must be accompanied by rupa. There are several suttas that state “vinnana cannot exist without rupa”. Since I am on travel, I am unable to find those suttas.
In terms of paramatta dhamma, citta and cetasika are represented by vedana,sanna, sankhara, vinnana. Therefore, at (Pari)Nibbana, mind (thoughts with citta and cetasika) also cease to exist, when they become detached from rupa.
Nibbana is an asankata dhamma. Everything in this world is a sankata. Nibbana element does not exist in this world.