I've used this method successfully as a workaround to Ubuntu 14.04 Bug #1317288 (clock disappears from Unity panel).
I followed the instructions from the link above, reposted here with my bash script.
From a terminal, install indicator-sysmonitor:
sudo add-apt-repository ppa:fossfreedom/indicator-sysmonitor
sudo apt-get update
sudo apt-get install indicator-sysmonitor
Start the indicator
indicator-sysmonitor &
You should now see a cpu and memory indicator in your dash panel.
Click anywhere on the indicator to open its menu, and select "Preferences". In the "General" tab, enable "Run on startup:"
Go to the "Advanced" tab and click "New".
Name your new sensor "clock", give it a description, and type the following code into the "Command" field.
date +%a\ %b\ %d\ %r
Click "OK"
On the "Advanced" tab, in the "Customize output:" field, delete cpu:{cpu} mem:{mem} and type
{clock}
Change the update interval to 1.0, and click "Save".
You should now have a day + date + time indicator in your Unity dash panel.