Depends on what kind of event is it. And what's the lighting around there gonna be like.
Hwever assuming that it's a speech like event, Best is for you to bring 2 lenses.
a Zoom ( like the one you got ) for close ups and a wide angle one for group shots etc
preferably one with a large, constant aperture like the 2.8 you got there, as indoors usually mean low-light. the 70-200 will not give you the ability to take wide shots. bring another zoom, maybe the 16-35 or the 24-70.