Unless I'm reading it wrong, it's not necessary for all copies to have bit rot, just the canonical copy that either Palatinus or Marsee had. Perhaps you are correct if by 'downgrading' it means the existing nodes out there--the 10000 copies you mention--would, by nature of the P2P network, becomes the majority again, but it's not clear since the mere fact that Palatinus and Marsee uploaded their nodes with a post-0.8 chain made the chain unstable. So it implies that two people--Palatinus and Marsee--had control of the entire bitcoin network by virtue of having a canonical node(s). Thus if these two nodes had bit rot, they would break the system.
No, because that's where the mining process comes in. Every block is validated with the hashes. Any "rot" would invalidate one person's chain and someone else's copy of the chain would be used.
Perhaps another way of looking at this problem is the gitbhub thread below. If, as the chief scientist G.A. claims, it was only due to the heroic efforts of two people to downgrade to a earlier version of the
BTC blockchain that saved the bitcoin P2P network from disaster, then it stands to reason that bitrot could cause a repeat of this incident, in that a 'buggy' version of the bitchain is adopted (namely, one with bitrot) and if there's no heroic people to step in, the system crashes.
Another way of looking at it: RAID systems have on rare occasions had bit rot that propagates, bringing down the whole system. In theory this is impossible, but in practice it is not. Might the same thing happen with bitcoin? Time will tell. I'll leave the last word to somebody else.
TonyT
The blockchain has anti-tempering code embedded inside. It protects it from easy modification. One has to spend a significant computing power in order to add a block. This catches any sort of modification: whether voluntarily or accidental. A bit rot is a random change - it will be detected and rejected.
The event you mentioned is of a different nature. Half of nodes were running an incompatible version of the software and were actively pushing a blockchain that the other half would reject.
In one case, it's an isolated incident that can be caught by the hash. In the other case, it's a widespread software bug that affects a large number of nodes - as if they all went crazy.
We don't have to worry about bit-rot. On the other hand software bugs can be a real threat.
These guys run mining pools. They represented a big portion of the hashing power at the time. They were running the good version but downgraded to the bad one so that the majority would be clear. In any case, it is not a single machine.
PS: RAID drives are not as well protected as the blockchain. It's a trade off between performance, space and cost. They could detect bit-rot better but they would run slower.
