Their architecture is not fault-tolerant. If one server goes down and the whole system goes down, then it was not designed to be fault-tolerant.

I have been running fault-tolerant systems spread across multiple dedicated servers (inside system with multiple DB/KV stores distributed/replicated/sharded, Kafka etc). If one server experiences hardware failure, the system will automatically recover within seconds to minutes (depending on which server/part of service failed) without any data loss.

It's not that hard. You need the knowledge, but it's not rocket science.