"...will the build fail when that path cannot be found?"
The deploy won't fail, the deployment will simply be unable to pin the applications because the applications don't exist yet. Since hese taskbarlinks would be generated before the state restore phase where applications are actually installed, the setup will be unable to create taskbarlinks as it would unable to locate the files, and you get nothing. So put office in the image, and use the code below.
Below is how one would pin a windows app to the start menu by default in the answer file.
<Link0>%ALLUSERSPROFILE%\Microsoft\Windows\Start Menu\Programs\accessories\sound recorder.lnk</Link0>
<Link1>%ALLUSERSPROFILE%\Microsoft\Windows\Start Menu\Programs\accessories\sync center.lnk</Link1>
While it's quite easy to use unattend.xml to assign links to applications in c:\winows\system32 like the snipping tool, sticky notes or the calculator, it's trickier getting Office in there.
What is far more reliable is the Office Customization tool to at least create desktop icons for office installs (Not the taskbarlinks, but it works.)
Check this workaround out here: http://www.youtube.com/watch?v=1Olg3uVqwD0
However, if you're really adamant about taskbar links, there are plenty of scripts that do this.
The best script I've found is here: http://theitbros.com/copy-taskbar-icons-windows-7-sysprep-v2/
If you're not a huge fan of scripting things like this, another option is using a "hybrid image" that has just updates + office in it allready, and try running sysprep a second time with a new answer file that then points to the allready installed office, that may just work too.
If Outlook is allready installed in the reference image, This works. I verfied this only works when outlook is in the reference image. The only time I could pin Office apps is was if they existed allready in the image.
%ALLUSERSPROFILE%\Microsoft\Windows\Start Menu\Programs\Microsoft Office\Microsoft Outlook 2010.lnk