Seems like a good lesson on why you should use backup options.
Also, if files are gone then they were deleted from the temp folder of windows. Otherwise, you possibly can find them back there.
Don't save on USB key or virtual drive.
Prefer saving directly on hard-drive. Save often and don't strictly work on a single capx, makes new instances as often as possible.
In the end, it's more a user bug then a Construct bug. Crash happens. Fail saved also do.
Use the best practices.
Better to learn it soon and lose a barely started project (2 days is ok and can be redone quite quickly) then later on.