Though isn’t it a case now, that nodes that are cut off from the network temporarily still retain the chunks they have? If so, the temporary shut downs might actually increase the data’s chance of survival in the World.
Let’s say a temporary shutdown includes 4 of the 5 replicas. The 1 replica is still in the network and it is replicated so that there are 5 again. On top of that, there are the 4 replicas in the nodes that are temporarily cut off from the network, and the data’s replication count in the World is raised by that 4 that are in the nodes that are temporarily out of the network.
On the other hand if the network holds 35 EiB of data, the probability of all of the chunks remaining after 1% loss is 33%. After 2% loss it is 0.
These number are easy to whip up, but really meaningless if they are not compared to other systems. I have had some data corrupted in a cloud service, and I would not bet on the data on some old, random hard drives in my closet to have much higher chance of surviving. But that’s about the comparison I can make.