With the right BGP and ospf design you can absolutely meet five nines availability for an end user customer perspective. We have some places that are approaching six nines.
This article reads like they had 1+0 everything and ran into a nasty iOS bug. Running out of ram is amateur hour as well.
When we need to do customer service impacting maintenance that will totally take their segment off the net, the hit can be from 15 seconds to a couple of minutes. And that is in a case where a colo customer is single homed to a single aggregation switch like one of our 48-port 10GbE aristas.