Failback of virtual machines is a manual task in vSphere Replication.

After performing a successful recovery from the primary site to the secondary site, you can perform failback. You manually configure a new replication in the reverse direction, that is, from the secondary site to the primary site. The disks on the primary site are used as replication seeds, so that vSphere Replication only synchronizes the changes made to the .vmdk files. Before you configure the reverse replication, you must manually unregister the virtual machine from the inventory on the primary site. See Replicating Virtual Machines Using Replication Seeds.

Automated failback is not available in vSphere Replication.