Hi,
WCL uses timeout to detects when serial device disconnects. So you do not need to monitor serial ports to detect disconnection. However, with some USB->COM adatpters we faced such issue and are working on this matter. Hopefully we will have solution soon. The problem is that some USB->COM (or its drivers) don't notify high level apps about device disconnection (when it is used).
Any way, try to not use monitoring and wait for OnDisconnect event from wclClient.