<$0.02>
On the subject of non-operational gateways I would consider attempting to send RIP broadcasts to them at a reduced rate instead of deleting them. In my case I'm on a dynamic address. It doesn't change often, longest I've had an address was about 5 months. It's most apt to change if I restart. I registered my gateway in January... it was down all of Jan and Feb. It's been intermittent but mostly down since until Monday evening of this week. Had my gateway been deleted or removed from the list I'd now be offline rather than online.
With my findings on some ISPs deploying CPEs in which systems filter (even on a DMZ level) all protocols with the exception of protocols: 0, 1, 6, 17, 41 (and possibly the IPv6 suite of protocols) there's many who don't know that they're being filtered since this affects inbound only. Outbound connects via ip protocol 4 appear fine to them. RIP broadcasts, since they're sent via ip protocol 4, are by default filtered so they won't even hit an ampr rip daemon.