@024f08ef 
Ah, I see.
If the registrar disappears, they'd usually transfer to a different one.
If that doesn't happen, the registry will either act as or appoint a registrar of last resort.
Basically transferring your domains to a different registry.

The only time that hasn't happened, that I know of, is when a country has unilaterally revoked a registrar and all its domains (Mali).