MusicLevel

local iVolume;

func Initialize()
{
  iVolume = 100;
}

func Timer()
{
  iVolume--;
  MusicLevel(iVolume);
  if(iVolume <= 0)
  {
    Music();
    RemoveObject();
  }
}

Script for an object which will fade out background music: the "Timer" function will decrease the volume step by step until it is 0. Then the music will be turned off and the helper object deleted.