I think some people here are confusing a maglock with an electric release. A maglock is a big electromagnet attached to the (usually) top jamb of the door. There is a corresponding steel plate mounted to the top of the door. When the magnet is activated (usually 24VDC) and the door closes, the plate is held by the magnet, thus keeping the door from being opened.
Various methods are used to allow the opening of the door, all involving the interruption of power to the magnet such as a motion sensor or a RTE (Request To Exit) button. Note that there are no mechanical ways to open the door. So any panic bar that may have a latch and strike must also turn off the power to the magnet first. Usually contacting the bar activates a RTE function.
Usually a fire system will turn off power to maglocks when it is activated, allowing the door to operate and be secured conventionally by panic hardware during the event.
Obviously a power failure will result in a "fail unsecured" situation, falling back to the normal panic bar locking operation. Many maglock power supplies will incorporate backup batteries.
-Hal