Why does the European MALE RPAS UAV use twin engines?
According to the Airbus press release:


  The MALE RPAS is the first unmanned aerial system designed for flight
  in non-segregated airspace and will be capable of performing a range
  of missions in intelligence, surveillance and reconnaissance, both
  wide area and in theatre. A twin-turboprop propulsion system will
  deliver energy for the mission system and provide proper redundancy to
  limit restrictions when operating over European densely populated
  ground and unrestricted airspaces.


Essentially, the aircraft is intended to be operated in the same airspace as existing air traffic, over large urban areas. The twin engine configuration is to provide redundancy and thus stop a robot plane from crashing on people.