> 1. I would get a proper SSL cert signed

Uh, how? Are you assuming that a single BGP leak would be enough to cause e.g. a letsencrypt misissuance for the domain? It sounds like (from other comments) they have a global round-robin resolver setup for their DNS challenges.

> 2. Only hijack one of the ranges, and do not respond to other domains (causing SERVFAIL), so other domains will resolve unaffected

I think exactly that's what they did. I saw people posting SERVFAILs during the outage.