When Gametracker banners are down for maintenance (which seems to be VERY often lately...) is there any way to show a generic banner showing the server's connection address and name rather than "Banner under maintenance"? Lately its getting to the point where the failed banners are more often than the working ones it seems.

While GT has been "down for maintenance" more frequently recently, it is not in this state nearly anywhere close to your claim. If you feel you are experiencing it this much, please try clearing your browser cache if it is caching the images for too long.