I think you meant Interplay lost the rights. That French fuck who killed the company still had a deathgrip on the rights to the Interplay name. I think Brian Fargo was negotiating with him or his rights to the name were going to expire. He said he might be getting the company name back.
The entire Fallout Universe was designed and conceived of without Chris Avellone. He came onboard with Fallout 2. Also, Obsidian didn't get all of the Fallout people. Some went with Brian Fargo to Inxile Entertainment, Microsoft owns both companies now.