It's a valid question, even if your scenario isn't plausible. The very point is that all data is ephemeral - there is no "data at rest" to be compromised. But the problem is that this data is very, very important. It would include (among other things) account information. If all of the servers power off simultaneously (for whatever reason), then yes, it would likely destroy them. More likely is a software fault that causes each system to crash, or lose/corrupt that data.

But there are ways around this, too. I have no idea which (if any) of these they are doing, just that these are options. They already probably sync data among running servers, it will just now be done exclusively in RAM. They can have "seed" distributed servers, running an entirely different codebase, simply to house this data. They would also be diskless, but mostly unconnected to the standard operational servers. From an architecture and design standpoint, these would work a lot like disks.

Distributed is also a key word - it wouldn't be a single server, rack, or even datacenter that would need to collapse. It would be to be all of them, or at least sever their connections to each other.

(Side note: Going diskless addresses concerns about data security for data at rest. It does nothing about data in motion)

TL;DR: Theoretically yes, but it would take a lot more than that.