Uninstalling and then reinstalling your iTunes should also get your Bonjour reinstalled.
For the reinstall, use an installer downloaded from the Apple website:
... or you could get it back via your Apple Software Update for Windows.
Under normal circumstances, an uninstall/reinstall of iTunes doesn't touch your content. (That being said, it's still always a good idea to maintain a current backup at all times in case of disasters.)
If you'd prefer not to uninstall iTunes, try the following procedure.
Download and save a copy of the iTunesSetup.exe (or iTunes64setup.exe) installer file to your hard drive:
Download and install the free trial version of WinRAR:
Right-click the iTunesSetup.exe (or iTunes64setup.exe), and select "Extract to iTunesSetup" (or "Extract to iTunes64Setup"). WinRAR will expand the contents of the file into a folder called "iTunesSetup" (or "iTunes64Setup").
Go into the folder and doubleclick the Bonjour.msi (or Bonjour64.msi) to do a standalone Bonjour install.