Again, from https://safenetwork.wiki/en/Vaults_(How_it_works), and again with the proviso that this may not be completely current,
"Once consensus is reached, the DataManager passes the chunks to thirty-two DataHolderManagers, who in turn pass the chunks for storage with DataHolders. If a DataHolderManager reports that a DataHolder has gone offline, the DataManager decides, based on rankings assigned to Vaults, into which other Vault to put the chunk of data.
This way the chunks of data from the original file are constantly being monitored and supported to ensure the original data can be accessed and decrypted by the original User."
This raises the question that you are getting at: Sure, if a vault goes offline, then the data is reallocated. But what if only some chunks disappear from that vault? Do the DataHolderManagers recognise this?
I’m somewhat certain that they would recognise, but am not 100% sure they do, or how they do. This is a question for devs, or forum members that know more than I.
The ID by itself gains you nothing. Over time, as you serve data, and behave according to the network rules, your rank increases, and with that increase, your yield in SAFEcoin from GET requests. Switching off resets this (as you now have a new ID), and so your income level will be starting from scratch.
No, your previous income isn’t wiped out. Farming nodes earn income according to an algorithm that includes how highly they are ranked. Ranking develops over time. So you are starting from scratch every time you get removed from the network, or you drop your vault and start over. Your income then falls to the lowest level (far below network average).