Hi,
I will try to answer this.
I am not sure how you program your ipad/crestron to communicate with the codec, but if you codec is connected to the crestron, you should be able to program the crestron to terminate the call via the codec API commands or available crestron commands (if any) that works with MXP.
For example, the API command to disconnect call is "xcommand DisconnectCall". It doesn't matter if the call is initiated from the TMS.
But if it is a TMS schedule call and the end point drops out halfway in the conference, you might get a prompt on screen to reconnect the call. Then your crestron has to be programmed to either let the call reconnects or terminate the call.
regards,