Is there any way to know device in the network is live or dead??

You can try to send active endpoint request to all of the nodes periodically. If there is response, it means the node is alive. Otherwise, it's not or out of radio coverage.

Sir ,

As you said Link Status cannot be used for checking whether the device is Alive or Dead (whether in the network or not). I am still hoping to persist you that we can potentially use it. Kindly let know your thoughts based on setup explained following,

I have a CC2531 connected to BBB through USB. I am using ZStack Linux Gateaway and ZStack Home for this. I have another USB dongle being used as Sniffer. "Link Status" is something we automatically keep receiving at CC2531 (Coordinator) since that activity is continuously going on by default. I want to find a way so that I can carry this "Link Status" data from CC2531 (Coordinator) to the Gateway Client running on BBB. So that I need not to implement anything additional for checking whether the device is Alive or Dead. I do not have a good command at Coordinator Side (ZNP). Since we know that we have options like zcl_SendReportCmd() for carrying the sending data from ED or Router in the network. Is there a way generally that I can send data from Coordinator to the Gateway Client running on BBB ? (I mean there is communication between Coordinator and Gateway Servers through USB pins/UART pins, but I dont have the source code for that, so that I actually send the data directly from Coordinator to Server and then to the Gateway Client)