To answer your question, plenty of things can go wrong...:eek3: To not replace the pads was an unwise decision. The squeaking you heard earlier was the wear indicators built into the pads...they're designed that way for a reason- to let you know the pads need to be replaced pronto.

It sounds like you've worn the pads through the backing, and this should be avoided at all cost. The rotors are probably deeply scored now, and will probably need replacement. You may have also damaged the seals on the caliper piston, which will only further increase the cost of repair.

From what you've told me, the car is not safe to drive at all. Given the circumstances, and my estimation of your abilites... I'd recommend having the car towed to your mechanic for the requisite repairs.