1996 Mercury Sable brake pad fell out

If your brakes have worn to the point where parts are falling out you're way past due my friend! Merlin is right, however he didn't answer your second question which really serve the opposite of what this site offers which is avoiding trips to the shop and saving money. If the brake caliper fell off and the pedal went to the floor then you must have lost wheel cylinder pressure. You'll know this especially if you have brake fluid leakage and it will be noticeable. You should replace the brakes as well as the wheel cylinders since you waited so long - not only do they often go bad after about 50K but once you lose a component under pressure it will usually blow the cylinders right out of the gaskets. They are only about $15 a set so it's worth it and much safer than trying to re-pack them. Another important mention is that your vehicle likely has the type of rear brakes which have parts that need to be machine pressed on. These a real pain not only to get apart but to press back on evenly; Ford Motor Co is notorious for difficult brake replacements so if you haven't done many jobs like this before I would agree with Merlin and take it to shop with the appropriate tools for the job.