To my knowledge there's also ways to integrate network observability tools (like kentik) to automate this to a degree, for those that are big enough or DDOS events are common enough that is useful to do so.

I imagine getting paged because of a DDOS is slightly easier when it's telling you it already null routed a few IPs so the rest of your network isn't screwed and you just have to identify how problematic those specific IPs being out of service is and whether you need to take action or wait for them to get bored.