Could the owner-registrar of the domain lose ownership of same?
Yes, in any of the following circumstances:
When you lose a dispute about the domain in a case taken to ICANN (organism charged with supervising the domain registration system on a worldwide level).
Where the payment is not valid, is returned or is fraudulent. In this case, the domain will become the property of MrDomain.
Where the domain expires due to non-payment of the amount due for renewal of same. In this case the renewal will remain available until an interested third party registers it.