Aaaaaaaargh!
Don't worry, Simon ... even if they restore the redirect, it still won't be useable!
Because you can now only log in to Medicare using your MyGov ID (which is a completely-impossible-to-remember-random-sequence), then link this to your Medicare account. Unfortunately, having just tried this, the Medicare site won't accept your password as valid; and using the link to reset your password won't work either, because the email with the password will be sent off into the ether somewhere (it's neither in the inbox nor the spam filter).