Yes, I suggest they divulge the intellectual property. Games are an art form similar to paintings or music, and we as a society should be able to experience previous art.
Keep the IP while you run the servers and sell the game, when you are no longer interested in running the servers, drop a tarball of code. It doesn’t need to be simple, it just needs to be possible and complete. The community can take care of it. If the IP is valuable, then you have your incentive to keep the game playable until it isn’t valuable to you.
There can be a lot of interwoven licensing with games. fmod, speedtree, SDK terms, music... you can't just open source it in most cases and call it good.
Keep the IP while you run the servers and sell the game, when you are no longer interested in running the servers, drop a tarball of code. It doesn’t need to be simple, it just needs to be possible and complete. The community can take care of it. If the IP is valuable, then you have your incentive to keep the game playable until it isn’t valuable to you.