I had this happen (funny enough that's how I really got into it... well not so funny in retrospect I guess). I ended up having to use a drop catching service to recover my name. You don't really ever own the name, you're technically leasing it for X years. Having to pick it up off drops or similar (some registrars dont drop anymore and take ownership and auction off) is worst case scenario. I hope you mean the reseller has gone out of business then you can contact the actual registrar, but registrars going out of business is rare and normally someone intervenes (I recall directi doing this at some point but my memory is a bit vague on the incident) and takes over control.
When you purchase a domain from a domain registrar then the domain ownership still remains as you, but you cannot access the domain unless and until the domain is transfered to a working registrar. Since the company shuts down then the connection with the domain breaks at the time of renewal. Till then the domain works.