Without the "que" it's not the same phrase: "ele veio. depois você saiu"("he came and you left.") With the "que" is like "you just left and he came". Sorry, it's very confuse to me to explain, i hope you understand.
Well, where I live we pronounce DE like gee at the end of a word or when it is by itself as a preposition (of). The others are normal "de"