Virtual world has the potential to become a future global electronic market. It integrates many isolated markets in many areas. To achieve this goal, future virtual world is required to be persistent, which means that a virtual world together with its accumulated content shall exist forever regardless of dynamic changes of its virtual world users and virtual world owners. This paper addresses the persistence issue by proposing a decentralized redundancy model which is immune from the possible collapse of virtual world. The core work in this model is the selection of a redundancy level, which is based on cost optimization. The simulation results show that the proposed redundancy management approach is optimal compared with existing approaches.