Yes, this diagram has no redundancy. If a server crashes, nothing takes its place. Redundant pairs don't do extra work for performance, they are doubled to handle a server crash. The scale-out layouts are orthogonal to redundancy setups.
It means that in any non-Edge non-Maker organization of Ignition servers, where an Independent (non-redundant) Gateway is shown, a redundant pair could be used instead.
There are so many possibilities that I can't really answer that. Perhaps you should share some real-world application specifications with IA sales engineering. So you an get an official answer for your actual situation.