You don't need to use a TCL policy to do what you want. You could use an EEM applet. It all depends on the version of code running on the router as to what event detector you can use. If you are running 12.4T, you can use Enhanced Object Tracking to see when the E3 interface goes down, then admin down the GigE. For example:
track 1 interface Serial0 line-protocol
event manager applet watch-serial
event track 1 state down
action 1.0 cli command "enable"
action 2.0 cli command "interface gi0/0"
action 3.0 cli command "shutdown"
action 4.0 cli command "end"
action 5.0 syslog priority errors msg "E3 interface has gone down; shutting down GigabitEthernet0/0"
If you are not using 12.4T, then you could replace the track event detector with an SNMP event detector. In this case, though, you would need to know the ifIndex of the E3 interface. You can use "show snmp mib ifmib ifindex" to get this value. Then do something like:
event snmp oid 1.3.6.1.2.1.2.2.1.8.333 poll-interval 60 get-type exact entry-op ne entry-val 1
Here, 333 is the ifIndex of the interface you want to watch. The rest of the applet would be the same as above.
