With all the vagaries of bankruptcy law, many businesses will declare bankruptcy, "reorganize" their company, and continue on in business... usually involving firing a bunch of people and being forced to sell off any unnecessary assets.
Or, an investor could come in and buy up the company assets (with the purchase $$ going towards the debts that led to the bankruptcy in the first place), and take over the company operations.
Either way, the bankrupt company can continue to exist... and I'm sure there are many other variations on that theme.
I'd assume with a registrar, they'd be required to give notice to registrants wtih sufficient time to transfer the domains.