I wasn't aware that Chris O'Brien owns half of The Paracast
Well I spoke to Chris myself in the months just before he left. He was really frustrated because he was supposed to be an equal partner with 50% ownership but Gene never gave him a share of the revenue from subscriptions or adverts yet expected him to do the majority of the work.
The impression I get is that it wasn't a formal contract, more of a gentleman's agreement which is always risky even if the partner is not a conman like Gene.
He did most of the work for the show and was supposed to be a partner but got nothing in return except being tarnished by Gene's worsening behaviour.
Listen to any episode from his era and it is he who does most of the interviewing, it is also clear that he is the only one that read the book or researched the topic. According to Chris, he was also the one that lined up the guests and arranged the interviews. The only thing Gene did was count the ad breaks and interject his stories about TV shows and people he knew.
In all honesty his contribution could easily be removed and those shows would actually be better. I doubt he even did any editing - knowing him he farmed it out to someone in the developing world like some other podcasts do.
So in theory, Chris might have some kind of claim on those episodes if they are sold (which personally I think is doubtful). Gene being Gene he would probably have to take him to court to get his share though and as others have said Chris seems to have decided to just make a clean break.
I don't blame him. Sometimes when you have been parasitised by a scumbag for a long time, the best thing to do for your own sanity is just cut off all ties and get away.