It's already built-in to the Ethernet I/O Scanner. By default, the PLC will flag a FATAL error if it loses comm with a slave.
You can actually DISABLE that functionality on a PER SLAVE basis for non-critical slaves, or for manual control of flagging fatal errors via logic (e.g. you write your program to have 2 modes, MAINTENANCE and NORMAL; during MAINTENANCE mode of your application logic, ignore slave error bits and stay in RUN mode, but in NORMAL mode, have the slave error bits drive a STOP instruction).