Because the first poster missed the point of the question(not how to redirect, but how to detect the status of the server), all other seemed to miss this point in one way or the other. The few(one?) who caught it seem to miss the other point(not redirect yes or no, but redirect in response to the status of the *other* server) and follow the herd who suggested ErrorDocuments. My Question is now:
Does the tone of the already posted responses influence the reading of the question? And if many monks err, does one want to correct them or let them correct oneself?