Dodora, an ICANN-accredited registrar, has had its ‘operations’ frozen, and its names migrated by the bankrutpcy receiver to Directi, according to this Directi announcement. 

This ICANN Watch piece indicates that Dodora was associated in some way with spamming.  This Domain Name Journal page indicates that Dodora has ‘long been a source of consumer complaints.’

I’m aware of registars being sold (NSI being the largest example) and registrars being merged (SRS Plus, where I’m a re-seller, was merged into NSI), but I am not aware of another instance of a prior instance of a registrar going bankrupt, necessitating the migration of the domain name registrants.  Email me if I’m wrong.

An anonymous comment posted to the ICANN Watch piece states that ’50 to 75 registrars have indicated that they will go out of business’ (there are over 200 accredited registrars, although not all are active).  Does anyone have more info on this?