Ouch... well, obviously the barn door is open and the horse is long gone.
The first option is to hold down the Alt or Opt key and start LR - this will force it to ask you which catalogue you want to open and you can direct it to the restored catalogue.
Did you back up the metadata to the files or is it all held in the catalogue? If you backed up the metadata you can create a new catalogue, import the images and LR will read the metadata on import. You'll lose a few things like Collections and flags, but you'll gain most of it back.
If not... hmmm... What MIGHT work is this. LR creates a different folder for each catalogue so what you could do is create a new catalogue with a different name - Catalogue 2 or whatever, and reimport the images, then close LR, go to your file manager and copy the subfolders (previews, etc.) from the old catalogue folder into the new folder, overwriting what's there. Then restart LR. I don't know if that would work or not, but it might be worth a try.
Mike.