eh, kinda? Decentralisation means one instance can learn from the failures of another, and there's bo one thing that can bring the entire Fediverse down. But that's a worst case scenario.
What I fear is this: A spike of interest in the fediverse leads to many instances being overwhelmed, and the general newbie experience quickly turns many people away, leading to lots of people leaving with a sour taste. In the meantime, instances successfully adapt and new ones spring up, but most users aren't coming back.
Imo that's a more realistic scenario than some grandiose failure, and you could say it's already happened several times.
Well yeah, that's what being overwhelmed means