Restoring a backup will set your LR back to the time the backup was created. All the work done since then will be lost.
Did you delete the original RAW files? Why are your images now jpgs and not RAW anymore? The export does not change/replace the originals you imported into LR. I don't really see the issues - they still should be there.
Are there any '?' on folders or '!' on photos in LR library?
An export is not a backup. From the LR point of view, use the integrated backup function to backup your catalog. However, this does NOT include and backup the photos itself. You need to backup the photo RAW files separately - LR has no function to do this.
Upon import you can select to have LR make a backup copy to a second drive for instance - that would be a way to backup your RAW images.
Your images are not IN LR.
LR is a database program that only makes a reference to where your images are stored on your hard drive. It also does not change those images in any way even after doing multiple edits to them. The only time the edits you make are actually saved to an image file is when you export it.
So restoring a backup of the LR catalog file from a previous time will not bring back all your original files if you have already deleted them.
All you will end up with is a catalog file, a database reference file, that has question marks ( ? ) next to the images.