I have two rigid bodies (they both are small hierarchies actually) and attached them to each other using a 6dof joint with all limits locked to zeroes.
One of the bodies is controllable with left-right keys, there is a motion actuator that does simple rotation.
I start a simulation, do the rotation, wait 5-10 seconds, and the joint detaches by itself. The second body stands still in the air.
The scene file is here download blender scene