I don’t say servers don’t exist. Cloud infrastructure has a cluster of machines behind it, is not magically, the CPUs and memory needed to compute the software must exist physically somewhere. Directly owned by Blizzard or rented to an external provider, but it must exist somewhere.
I just said that the classical beliefs everyone has on their mind that a server is a physical machine someone can physically touch do not exist. There are physical servers but you can’t identify a physical machine and say “that machine is Silvermoon realm, to others are not”. There are realms, there are virtualized servers and there are physical machines, but all three of those things are unrelated, you can’t identify one piece of hardware and say “that machine is Silvermoon realm and server, the others are not”. Server and realms are not things you can touch anymore.
By the way, others can flood into shards and people from those 2 can’t for one simple reason: to be able to switch shards you need to be connected in one shard in the first place. So, if all Silvermoon shards are collapsed and Silvermoon players are assigned to those shards upon login they won’t be able to play, but any of those players that before that happened were playing with other people on shards assigned to other realms or inside dungeons will be able to keep playing normally while their realm shard is not available.