How can I restore a deleted Download folder in Finder missing

Is it also gone from Macintosh HD > Users > You > Downloads?
Have you looked via Spotlight?

If so, you should stop all writing processes to you Mac and get Data Rescue 3 (99USD), which is able to restore data which has been trashed but not yet overwritten by new 1s and 0s.

 

I'm betting it is still in Macintosh HD/Users/UserName/Downloads
but just missing from the Dock.

So...

Open the above and drag the Downloads folder to the right side of your Dock. It will not move the folder, just make a shortcut to it.

Now, a secondary click* on the icon in the Dock will give you options for displaying it. Play with those and settle on the one you like best.

*right or control-click

 

Restore Deleted Download Folder from FINDER

If you have accidentally deleted your Downloads folder from FINDER and you do not have it on the Doc.
Form Finder menu, click on "GO"
"Go to Folder"
type ~/
There you go. You will see the Downloads folder safe and sound.
Drag it back into Finder, right click and Add to Dock.