There are several references to how to replace lost icons, some of them
worked in certain undisclosed instances, while other attempts did not.
When you launch the LaunchPad from its found location, and it appears in
the Dock briefly and while it is running, (perhaps it won't?) you may be able
to Control + Click (to get tiny contextual Dock menu) to save item in Dock.
If that does not work, there also is a folder of those items and you may have
to find the hidden one where Dock items reside, and manually place a copy
there. That would probably make a symbiotic link, not quite an alias.
Or try:
•How to reset the OS X Dock to factory defaults:
http://www.idownloadblog.com/2014/10/14/how-to-reset-the-os-x-dock-to-factory-de faults/
{Note in the above page, a suggestion by DWayne Robinson (has image) shows an
AppleScript or shell. If it's applescript it may work in Automator. I haven't tried it...
For that item look into the Comments section below the above linked article.}
There are examples of 'shell scripts' that could be run to restore the default Dock.
However I'm not familiar enough with the look and feel of the script, to just run one.
So if you aren't I would advise against using them; one needs to know more first.
•Customize Your Mac OS X Dock with these Hidden Terminal Commands:
http://www.makeuseof.com/tag/customise-mac-os-x-dock-hidden-terminal-commands/
[There is a product called TinkerTool that can allow access to really damage an OS X.
Or if you know how to use what it can offer, it may customize the system.]
I'd try to launch the missing item and then see if the Control + Click brings up the
small Dock contextual menu option to add that icon to the dock. It can be used
to find option to remove an existing icon. So be careful. And then, there's the page
link on how to Reset OS X Dock, above.
Good luck in this matter! 🙂