Clovenhoof
Mongoose
I'm not an expert on gaming license issues, but intuitively I'd say it's probably just impossible to repeal the OGL. Of course they can abandon the whole SRD/OGL thing with 4E, i.e. declare any new stuff they publish does not fall under it, but they cannot say that 3/3.5 SRDs are not OGL anymore.
Either way, it shouldn't bother Conan in any way. The Conan OGL system is fine the way it is. It does its job.
D20 is by far not the only system that can make a Conan game work, either. Had Mongoose decided to make Conan run on MRQ (Mongoose RuneQuest), that would most probably work, too. But using D20 of course does make it easier to switch from other D20 games, and you can use a lot of 3rd-party material with no or very little conversion effort.
Either way, it shouldn't bother Conan in any way. The Conan OGL system is fine the way it is. It does its job.
D20 is by far not the only system that can make a Conan game work, either. Had Mongoose decided to make Conan run on MRQ (Mongoose RuneQuest), that would most probably work, too. But using D20 of course does make it easier to switch from other D20 games, and you can use a lot of 3rd-party material with no or very little conversion effort.