I accidentally removed it - it is as simple as adding 'wingpanel' custom command to the startup from inside the applications system setting menu?
Seems to work,but not sure if that is the 'right way'.
You can install eOS Tweaks and there is a section called Cerberus. Wingpanel is added by default there so that whenever wingpanel is closed or crashes, it starts automatically.
There is a program for it:
Run gnome-session-properties
.
You should see all the programs that startup automatically with new session.
You can edit it, so just add wingpanel and it should be alright. :)