How can a registrar discontinue its connection with a certain domain name?

How can a registrar discontinue its connection with a certain domain name?

In the Online system the registrar can refuse to extend the period of the rights of use, if payment for it is included in the current bill.

The registrar, in making changes to the domain name contact-person data, can resign from its status as a registrar. In this case, the domain name user becomes responsible for the payment for the domain name.