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If the registrar is an ICANN-accredited registrar, then if the registrar goes out of business, the usual procedure is that ICANN arranges for all the domains held by that registrar to be bulk transferred to a new registrar who has agreed to take on the domains.
If the registrar is a reseller, then you should contact the parent via whom the company was registering the domains.
Back-ordering is hazardous, expensive, and will mean a lengthy period when the domain is inactive. So it is always a good idea to have important domains registered for multiple years.