Failback of virtual machines between vCenter Server sites is a manual task in vSphere Replication. Automated failback is not available.
After performing a successful recovery on the target vCenter Server site, you can perform failback. Click Incoming and manually configure a new replication in the reverse direction, from the target site to the source site. The disks on the source site are used as replication seeds, so that vSphere Replication only synchronizes the changes made to the disk files on the target site. For more information on replication seeds, see Replicating Virtual Machines Using Replication Seeds.
Before you configure an incoming replication, you must unregister the virtual machine from the inventory on the source site.