I had a similar thing happen to my old white lude, came to a stop at a roundabout and one of the front bolts had come off and the caliper slid off the disc, no brakes at all! Lesson: never rely on someone else telling you they have done something without checking it yourself
I think you can get a rebuild kit cheap enough for the callipers its easy to do as well. The most common problem is the handbrake cam inside the caliper slipping over its threshold and resulting in no hand brake on that wheel. The only way to avoid that is to not let the pads get too low. If yours are at the point of slipping over they could be getting stuck in the vertical position something else that happened to me a long time ago i took the wheel off and hit it with a hammer, gave the handbrake a few yanks and it freed off. At least no one was hurt lucky escape I say. Finally, I used to have a ford cougar and the brake pipes corroded so badly they burst at a junction which I flew out of and nearly hit the wall on the other side 
that was another brown trouser moment, it only had its mot about a 3 weeks before 
bit hectic ATM and will be sent satdy.
