> What if DDB goes down

It's worth clarifying that question. What does "Go Down" mean? One region is down? Is it a bad software bug?

The database itself is fault tolerant. Nodes can go down all day without any real consequence. Each region is isolated, so a failure in one region won't affect other regions.

I guess I'm at a loss for the type of failure with DDB that would make it a SPOF, especially more than other datastores.

They introduce change one region at a time usually. DDB did have outage many times and brought half of AWS operations down. But good question how they kept Amazon.com alive if some part of their systems rely on DDB.

[1]: https://aws.amazon.com/message/5467D2/