As an update to this, I managed to replace the antenna. Here's how I did it.
I bought an antenna from a wrecked Volt online, it was about $100. It was grey and my Volt is blue, so I unscrewed the casings and switched them around.
I decided that it was too risky to try to drop the headliner and opted to go inthrough the rear dome light. Removing that thing was a huge pain in the ass. The outer casing was a pain because it's attached by 3 clips in one side and I still don't quite understand how it is actually fixed to the body because the clips didn't really make sense. Then the dome light itself is clipped into the roof. Its the same dome light as on a few other Chevy vehicles, namely the Silverado and I found a great guide on another model's forum with photos. You have to pry the clips out of the roof casing with a pry tool or a couple of screwdrivers and I found it to be pretty much impossible to do alone because you can't see a damn thing up there.
Once the light was out I could see the bolt where the antenna was attached but it was quite hard to get to, you can use a socket wrench but quite tough and tutoring to position. The bigger hassle is unplugging the two cables attached to the antenna, you better have tiny or hands or know a kid willing to stick his hands into an area with lots of wires because it is so hard to reach. But I managed to do it and managed to reattach the new antenna in the same way, but I can't stress how frustrating and difficult it was.
Now my antenna is on but it isn't flush to the roof, so my last question for the forum is any advice on how to get this thing flush? It is screwed in all the way. See photos.