When the secondary node becomes a primary node, it enables the task scheduler, allowing tasks to be run. It also begins accepting connections from MOVEit Central Admin. Because the other node is dead, the new primary node will initially not be able to replicate changes to it.
When the dead node comes back to life, it checks with the other running node before deciding whether to be the primary or secondary node. Assuming that the other node is still running in primary node, the formerly dead node will become secondary and will catch up on any changes made while it was down.