Fixed! Best buy had an adapter they called a reverse antenna adapter. It had the right connector for the stereo on one end so I cut off the other and soldered it to the factory wiring harness. Plugged everything back in and it's working again! Here's a pic after the fix.

Is the missing black part still stuck in the back of the radio? No, and I checked all around underneath and behind the dash in case it was dropped. The previous owner had installed an aftermarket stereo at one point so I'm wondering if it was accidentally pulled off and lost. The wire as-is doesn't...

New 2009 Vibe owner here and working to fix some issues. I removed the factory stereo to fix broken volume/tuner knobs (thanks for the great info on this board!) In the process I found the antenna wire is missing the plug on its end that goes into the factory stereo. broken_wire.jpeg Based on some r...