Based on this question, as well as based on your previous questions (e.g., here, here, or especially here), I get the impression that students in your school are leading the teachers on quite a bit. I have been teaching large undergraduate courses (400+ students) at a public university in central Europe for years, and many of the problems you often seem to stumble into are pretty much unknown to me. For instance, I can literally remember a single incident where one of my many students claimed that he could not finish his homework because he lost data due to a technical problem. You, on the other hand, make it sound like this is a regular occurrence.
As I don't think that your students are somehow inherently more prone to lose data due to no fault of their own, the logical conclusion is that they are (at least in the majority of times) just making up excuses. Hence, the question is not "how to deal with students who lost their digital work?", but rather "how to deal with students who claim to have lost their digital work?".
My answer to this question (and, incidentally, also to your other, previous questions) is to treat your students as adults. Among other aspects, this means that they are responsible themselves for any technical issues on their end, the real ones as well as the made-up ones. Yes, this will mean that occasionally, somebody will actually be struck by a problem innocently, but at a university, adults are supposed to handle problems by themselves. To me, this is a large part of the learning process at a university - there is no safety net that catches you when you are behaving unreasonably (and, yes, not correctly backing up your homework definitely falls into this category).
So, my answers to your problems would be (formulated a bit more politely, but no less directly):
Deleted entire project folder.
Too bad. Do it again.
Reformatted hard drive or upgraded system without backup.
Too bad. Do it again.
Sent computer to be repaired, cannot work on project until it returns.
Use one of the computers in the university lab, or borrow a computer from a friend.
USB not unmounted, files broken.
Too bad. Do it again.
(Also, speaking as a computer scientist, this is so unlikely to happen on modern file systems that I would be very much inclined to think that you are lying to me.)
Device containing project folder lost or stolen.
Restore from backup. If you have no backup - too bad, do it again.