Theymos would need to be properly served in order for him to have to show up in court. Otherwise any judgement against him would not be enforceable, and would be reversed.
You would serve the domain owner WhoisGuard, Inc.
Domain Name:BITCOIN.ORG
Registrant Name:WhoisGuard Protected
Registrant Organization:WhoisGuard, Inc.
Registrant Street: P.O. Box 0823-03411
Registrant City:Panama
Registrant State/Province:Panama
Registrant Postal Code:00000
Registrant Country:PA
Registrant Phone:+507.8365503
In some cases an In Rem action can be filed where you sue the domain name. Not sure if that is possible in this type of case. In any case service is not that difficult. If Theymos would need to be served at some point he has already provided enough info to find him via his Reddit AMA.
I am not very familiar with the laws regarding proper service as I have never had to try to avoid service like this. Regardless he would not need to personally appear in court unless he was compelled to testify, if he simply wanted to put on a defense he could have someone appear and speak on his behalf (an attorney/team of attorneys)