Actually, it only takes one full copy of the blockchain somewhere accessible. It's the Many-Copies-Keeps-Data-Safe method, and might mean that the blockchain is, or soon will be, more safe than the text of the Bible.
Of course, the network (or what's left of it) would then be extremely vulnerable to tampering. If there's only one copy, well, you'd better hope the person with that copy either doesn't know how to mess with it or doesn't want to.
that your's was the last copy.