Nowadays, you have a plethora of back-up options at your disposal: memory sticks, hard drives, clouds, Dropbox, etc. At the end of every writing session, even if all you did was adding a couple of sentences here and there, send yourself every document you have worked on via email and copy the files on an external hard drive. You can also email copies to friends or family members. Computers die overnight without advance warnings, hard drives can be damaged or stolen, so can computers. Being paranoid about protecting your texts will potentially save you a lot of pain and effort.