There would be some very questionable humor, screaming (and i kinda really miss Hunter's screeches from the second season. He was GREAT while raising his voice, no matter what anybody can say about it being annoying), grotesque episode scenarios, cool uniforms and much else!
After Dib dies, Zim replaces his computer AI with Dib's AI. He is more annoying than the previous one, but at least Zim gets to talk to Dib again
Then Zim leaves earth, because he understands that Dib is gone, and the computer is not really him. So he leaves his base to rot, and Dib to go low-key insane