I’d say those who know anything about farming rate will realise that the more the strong supporters turn off their computers the more farming rate rises and more the opportunity to earn extra coin.
Also you must consider that the earth is round and this will be a rolling “outage” So the effects will be not be the same as if all those who turn off did so for the SAME 24 hours
In theory the number could drop to 1. But the system tries for 6
Also as people turn off so then the chunks in the vaults for those who stay on will rise to compensate.
As long as enough storage stays online then it will remain at 6 even if 1/2 turned off. Its not the number of vaults but the total storage provided.
EDIT: Put some figures
massive turnout for earth day. 30% worldwide have turned off at any particular time. Like 50% in each timezone turn off for nearly 24 hours average each
If average copies prior to earth day were at 5.5 which is low and farming rate is 0.25 (TP-TS)/TP
Then at any one time 30% turn off resulting in 30% less storage ==> average of 3.85 copies
FR rises to 1.00 and everyone who doesn’t turn off realises they can “cash” in for 24 hours so they turn on extra storage/vaults and the number of copies rises and FR will drop again
At no time was the network in any trouble and that is with it starting with lowish storage and 50% of the world joining into the earth day turn off.