theBat gives you 3 ways to delete a folder
1 move to trash - moves everything to the trash folder
2 wipe - deletes the folder and the associated message base
3 leave message base intact - only deletes the folder from theBat view, but the message base remains.

So if you selected 1, just restore the things from the trash. If you selected 3, create a new folder with the same name and restart theBat, then it will show the messages.

But if you selected 2, it's harder. To check, see if there is a physical folder with that name under your
<mail folder>\<account folder>, and if there is a messages.tbb file inside. If yes, we have case 3. If not, check the Windows recycle bin first, I don't know if TB puts stuff there or deletes directly.
If nothing there, use some tool that can recover deleted files, there are plenty and your chances are good (in case your disk is not NTFS formatted, you may even try the DOS 'undelete' command first).  
Don't perform any file I/O operations before running the recovery tool, as this decreases the chance to recover the files.