Complex sentence: It is believed that the air ambulance suffered a decompression event as a result of the collision, disabling everyone on board, continuing on autopilot past Dakar, until it is presumed to have run out of fuel and crashed in the Atlantic Ocean.
Split into simpler sentences: It is believed that the air ambulance suffered a decompression event as a result of the collision, disabling everyone on board. The plane then continued on autopilot past Dakar, until it ran out of fuel and crashed in the Atlantic Ocean.