Lyric discussion by Yacusan 

Cover art for Goodbye Cruel World lyrics by Pink Floyd

I have always interpreted this as being pinks giving up, giving in, and becoming what he hates most. A fascist. Pink could not be around for that so pink is gone (dead, crazy, or locked behind the wall) and in comes the new character I'll call him Mr. Floyd If you will. Death and rebirth. A common thread.