Headphone plugs are known as TRS plugs - tip, ring, sleeve. These correspond to the left channel, right channel, and ground channel respectively. Each of these has insulators between them, to keep them from interacting with each other. Also, when you plug it into a jack, these plastic separators discourage the jack contacts from touching more than one of these at a time. So, there's a bit of working knowledge of a headphone plug. ;) As far as yours and how it will hold up, it's hard to say. I wouldn't worry about the gap around the insulator; if everything sounds ok, the insulators are still able to do their job, at least for now. Whatever caused the plug to bend may have put some strain on the internal wire connections - where the cable is soldered to the plug. But again, if it sounds ok, it should be fine, but these connections may have been weakened a bit and future abuse may have a bigger effect.
At the gym I do some running on a treadmill, and elliptical training; as careful as I try to be, occasionally I end up dropping my ipod or accidentally swinging my arm into my IEM cord, ripping it out and sending the ipod flying. This has bent the plug a few times, and I would just bend it back and things would be OK. But after this happened three times, the plug was damaged and I could only hear out of one channel, and had to replace it. If you have to replace yours eventually, it's not the end of the world, just a few bucks and a little bit of time.
PS Why does the post editor on this board suck sometimes? Often it won't recognize when I hit 'enter,' I can't move the cursor by clicking the mouse, etc.
