Do I or RR need dns clue?

Hi, Mail to RR users is getting refused due to PTR issues. I contacted RR and explained that yea, one of our 2 DNS servers for the IN-ADDR.ARPA is down, but the other is fine. They said that I should either get the DNS server back up (Which of course is already being worked on, was the minute it went down) or delete it from ARIN IN-ADDR.ARPA records. Isn't the whole point of multiple DNS servers that if one is down the other can still answer queries? Or am I missing something here??? Thanks, Tuc/TBOH