Comment by encryptluks2

Mullvad and similar providers often colocate or rent servers from multiple local hosting providers. A group of servers going down for them would not be a big deal. Network boot is not difficult/expensive. Many of their servers are using 10Gbit uplinks+ so I take it they get pretty good deals for bandwidth. It isn't like Amazon or other cloud providers that charge an arm/leg for egress.

The point of not using local disks is again fairly straightforward, to show that they do not have a stateful storage medium to write logs to. Whether it significantly helps or not is beside the point, they have determined that it helps provide assurance to their customers and additionally showcases a feature for auditors.

Network booting loads the OS into RAM, so even if there was a network outage they'd have to restart the severs to cause a problem. From what I know of most VPN solutions though, again a network outage would only affect the group of servers at that data center which isn't their entire operation.