Hello!
With GIMP, ye can open recently made files. Click "File", then "Open Recent" should appear- drag y'er mouse over it to see a list of recent art files. Y'er preset head should be close to the top of that list.
Also, I'm not sure whether ye mean ye deleted the line (preset guideline) file itself or the layer on y'er preset with the guideline. But, if 'tis the first, I'm sure ye can find it on the thread created by Buffy with each FH file separately available f'er download.