The obvious disadvantage is that the drone is programmed with a source and destination point which are easily extracted from the machine. Cleaver LEOs could probably get to the receiving point within the window when the drone is expected and, if not, the points are probably pretty close to their base of operations.

When interrogating a pilot the pilot can clearly signal distress to compatriots and is likely going to take longer to actually disclose their intended destination.

You could certainly program it to delete the source and destination once speed goes low enough far from the destination.