There is no addon that tells the clients on the server that it has crashed. If there was one, if they lost connection to the server, it would tell the clients as if it had crashed. Although, there is a addon that gives an option to the player that he/she has lost connection/ the server has crashed, it will try to reconnect them to the server. My friend has this on his server, he told me you can find it on facepunch in the addon release section.
