your caliper piston is not retracting, so that is why the inboard pad was gone and the outboard wasn't. It will not affect stopping power or cause the brakes to pull, because of teh high pressure when applying the brakes. The calipers return under only slight vacuum pressure from the piston in the M/cyl returning so they wont pull back in there bores, effectively wearing out the inboard pad. Double check the hose on that side also, as they can cause a similar situation, but it's a 95% chance of a bad caliper. As far as the parking brake keeping the brake light warning light on, you probably have a seized cable, due to most people not using their parking brake on an automatic. Normally bad calipers will cause the rear brakes to drag or no parking brake function.