[ab-dm]

I thought about this, and it can't really get any worse than 'total outage', so I thought it was worth taking a shot. It can't go any more down.

It worked for me, so once Heroku has sorted their s*t out and their DNS system is back up it's just a matter of deleting the A records and replacing it with the CName.

Worst case scenario is the underlying Amazon IP Addresses change and it goes back down.

[Trasmatta]

Wouldn't the worst case be the underlying IP address changes, and your site now points to some other service? Since Heroku doesn't offer static IPs, I don't think.

[cyral]

Heroku seems to use the Host header on the HTTP request to determine what customer the request is sent to, so I don't think it can end up somewhere it shouldn't be unless the IP leaves control of Heroku entirely and is picked up by another AWS customer.

[rsweeney21]

Heroku uses the host name to route requests. So you wouldn't serve another site, it would just give you an error that your site wasn't found or something.

[exitnode_ttl0]

There is one more problem I can think of (but yes you're right, it can't get worse than 'total outage'): Heroku might detect that the CNAME is missing and will deactivate some stuff from their automatic domain management / TLS certificate issuing.