I don't really believe this is possible, for a number of reasons, but it's an idea:
1a: Main location is down. People who try to visit it get a server error message.
1b: Main location is down. People who try to visit it get automatically redirected to clone #1.
2: Clone #1 has issues. Automatically redirects to clone #2.
3: Clone #2 works without problem. The requested channel/page can be viewed without problems.