I think this form will be taken care by the siblings of theymos. As with all the business, their ownership is never transferred to the external shareholders.
What makes you think he even has siblings? Unless he wrote about it somewhere on the forum. Considering how private of a person theymos is, I doubt he did. I don't think Bitcointalk is something those close to theymos will inherit. He didn't inherit it by being the child of the previous admin either. Passing it on to children or siblings should not be something he would seriously consider unless they have a major interest in bitcoin and forum management, and they are already on the forum without us knowing about it.