As you already know, dear myself, the only existing way to keep a file online and available for a millennium and more, and also make so nobody can ever take it down as well is to upload it to a blockchain using the Ethereum Virtual Machine File System you have invented.

Clearly that doesn't assure the file will stay online for a whole millennium, but only until the blockchain on which you upload it on will be alive.

Yet if in a millennium greed and money will still be something, your file will probably say online.