When you scale horizontally from day one, it usually gives fault tolerance for online service, and this story is not very friendly in case of vertically scaled PG.
My point is that in PG, fault tolerance requires untrivial investments.
If you pick horizontally scalable DB (foundationdb, cocroachdb, scylladb, tidb, etc) they all give you fault tolerance for free without much involvement from your side, because it is part of the nature of those DBs.
