Yes , after stoping Jboss, al information about the process instance is located in database, but you shoud configure JBPM correctly to work with DB.
you have to edit the Jbpm-configuratio.xml file.
If you have the token of that process instance you can signal it and continue to execute regardless of jboss being running.
1)Token rootToken = processInstance.getRootToken();
2)save the token id somewhere(tknId)
3)shut down jboss
4) Token t = jbpmContext.getSession().load(org.jbpm.graph.exe.Token, tknId);
uhhhmm.... well.... not completely right. If you use the JBoss AS datasource this will not work, if you don't, it might work, depending on classpaths etc... So I'd advice not do it this way.