the organization has two 2010 Exchange servers with the latest updates. I needed to set up hybrid work and do a mailbox migration. Since Exchange 2010 is installed on a legacy Windows 2008 OS, I made the decision to add Windows 2016 with Exchange 2016 to complete the Hybrid Configuration Wizard.
First, I installed the AD Connector and performed a successful sync on one of the domain controllers. In the course of setting up hybrid operation, I chose one from Exchange 2010 that was accessible from the external network. The setup was successful.
If I decommission Exchange 2016, I won't affect the hybrid configuration in any way. After all, it is configured for Exchange 2010, this old server was chosen in hybrid wizard.
Exchange 2016 was only used as a tool for hybrid setup.