Hydrazine as a reduction agent
I'm sorry for the wrong answer initially given; you might consider to unaccept this one.

I'm not sure whether this has ever been examined in detail. It is likely that nobody bothered to collect the (volatile) reaction products of hydrazine.

According to a procedure provided by the group of Rodney Ruoff (DOI), the reduction was performed in an open flask equipped with a reflux condenser. An aqueous suspension GO was first sonicated (to support exfoliation) until it became clear, then hydrazine hydrate was added and the mixture refluxed at 100 °C for 24 hours. During this time, the reduction product precipitated as a black solid. 

No remarks on what actually happened to the hydrazine were given in this article.