The drop of DCD will close the session, as long as, the cable is wired properly for the desired DCD functionality.
If you are using an 8-wire cable on the port, you will need to activate the altpin setting on the PortServer unit:
#> set flow range=(port_#) altpin=on
If you are using a Digi 10-pin adapter, this setting should remain off.
You can then monitor the signal activity from the PortServer:
#> display port range=(port_#)
This will allow you to confirm that the DCD is asserted and that it is also being dropped when the connection is closed.