Got lucky! Found the source folder in my Dropbox Deleted Files folder on the web!
Good for you!
I use a mix of backup solutions but I found all the automated backup systems I have tried to have issues. I had a hard drive crash last January 1st on my main machine and while I had most of my stuff backed up, it was a manual thing and I did lose some projects I had been working on during the holidays. A couple of those were for a paying customer so I had little choice. It cost me $1,200 to have the data exhumed from the hard drive. It turns out the drive had been running hot and the head was stuck on a platter. I was lucky the data I wanted ( a few folders) was salvageable but it was not cheap. It took over a month and by the time I got the data back, I had recreated almost all the changes. Somehow, I am more careful now how I backup. Funny how it goes...
I have a global backup using my Google drive account and Google backup. I do not like it too much so I have a second, manual backup for my important projects and for those I religiously and manually backup the day's work to the cloud before going to bed, no exceptions. I also duplicate all my software tools and projects on a second machine and I occasionally run it to make sure everything works. Now losing my main machine would be a minor event.
I do also use Dropbox for some things (like Word documents and spreadsheets) for the convenience of sharing between machines almost instantly, but I have found it is just about impossible to run my C development tools on a Dropbox folder. I suppose Dropbox' eagerness to backup files as they are created interferes with the compiler/linker's job, which is to touch, read, update and create a whole bunch of files in a hurry.