Sorry for the delay, I am often too scattered for my own good. 
I have been using the Endless 5 beta. In the Endless 5 beta you can install the Gnome extension manager from the software center. Using the browse tab you can search for extensions. There you will find “Another Window Session Manager”.
Configuration settings for the extension will allow you to setup save and restore session, so you can start back at where you were when you shutdown. That exension does not work with Endless 4. There is a save and restore windows that does work with Endless 4, but I found it to be useless.
So I assume as of now on Endless 4 there is simply no way to either hibernate or restore session, but on Endless 5 it is possible to setup a restore session, but from what I can see there is still no option for a proper “hibernate.”
Hopefully this will come close to meeting your needs