Yes. From within Lightroom you should notice the folder or folders have a question mark attached to them. Right click on the folder (control click on a Mac) and select "update folder location". Once the folder has been located then all the images inside are found again.

If you do not select the top level folder (lets say by accident) then that folder will remain missing and cannot itself be found but selecting the first child folder and right clicking will give you the option to "add parent folder".

Now, if the top level folder is not missing but all the others inside are you may want to select the top level and right click to select "synchronize folder". This will take a while with this amount of images as it basically runs a modified import. But at least all will be well.

And finally, the moral of the story is: Dont do things behind Lightrooms back. The folder panel is the same as the finder in terms of location and structure. You can move folders into others, create parent folders and child folders. All the while Lightroom is aware of what you are doing.

Hope this helps.