If HubPages shutdown on purpose, I would expect they would inform us in a timely manner. If it was hacked and taken down or a disaster happened and our hubs were lost, that's a diferent, if very unlikely, scenario.
Every one of my hubs (even the worst ones) are written offline. Always. No exceptions. They are after all, my property. My philosophy is: use the cloud but don't trust it. Even when I update a hub, I update my offline file first and copy the relevant section. Every hub has its own directory and in that directory I place all files related to that hub: the article file (containing the text, summary, tags and source links), image files, caption files associated with each image and any miscellaneous files. My offline "hub", therefore, is not a copy of my hub page, but I can update and add to it and recreate it if I have to.
PS (who uses postscript anymore?) I use Open Office/Libra Office as my word processor when writing. It's easier than online text entering plus bold, italic, http links, etc, all translate when copying and pasting into hub capsules without effort. I suspect the same is true for other word processors, though I don't know.