iRule to close an established connection

I'd try the custom user_alert option. Whenever the higher PG member comes back, you'll see the Pool member 10.0.0.1 Up log. With this, create an alert. Then use the "exec command=" feature to run delete sys connection cmd for your lower PG member. Hope this would do the trick. Try testing it with logger cmd to throw a dummy log.

alert higher_PG_Up "that high pg pool member up log" {
exec command="tmsh delete sys connection ss-server-addr 10.0.0.2 ss-server-port 80"
}

If the above doesn't work due to some syslog alertd daemon dependencies, try the icall method. That should definitely work. Keep us posted.