Lyric discussion by LondonPoet 

Cover art for Fader lyrics by Temper Trap, The

fader: a device for varying the volume of sound, the intensity of light, or the gain on a video or audio signal

A "fading" fader would be a fading control of stimuli, the things around you, or, more so, this world, the environment, and the conditions thereof. Hence, "this fable world's comin' down." Hold onto a hand because these cruel conditions are ahead, inevitable. This idea that we have (i.e. to say we are in control) is fading fast. As much as we talk about it, this talks floats along with us. They don't sink down into the depths and sod of Nature.

Also. jimcavs22 has good insight into a biographical understanding of this song that is think is important to note.

Song Meaning