BookDesigner makes beautiful customized lit files, which Calibre converts into beautiful epub and mobi files. I keep all my books saved as lit, epub, mobi, and htmlz files, and store them on an external drive as well as on OneDrive (and of course my C:drive). Keeping ebooks in various locations has saved my bacon numerous times, since 1986. From 5¼" to 3½" floppies to CDs to zip drives (remember them?) to DVDs to external drives to flash drives to the cloud --- my library has managed to survive numerous disasters and user stupidity over the years. Hell, in a fit of idiocy, I just installed the latest Madeira Linux to the "wrong" partition on my D:drive --- one filled with data. So my advice is obvious: save your ebooks in as many formats as you can, in as many places as you can. You may not think that something will happen --- but it will.
