Here's my opinion of what will really happen in the future of the "cul de sac". If things continue as they are
In the future, Kevin has becomed the unquestioned master of the world. He has raised taxes tenfold and placed mind control caps onto almost everyone on the planet, making them his helpless slaves. He rules the world with a dark heart with Rolf, Johnny and Jimmy as his minions. He has other minions too who are just as evil as he is (e.g Rainbow dash, Shadow)
He has banned christmas, laughter and joy in the world for everyone except him and his evil minions.
He took over the world by building a huge army of people loyal to him and ordering them to launch a huge attack on the world. Because his army was so huge and so evil, no one could stop him and he soon enslaved mankind. When he discovered the Eds were immunue to the effects of his mind control helmets, he made them his prisoners so that he could torture them every day for his own sick enjoyment.
Everyone was under Kevin's control because they had mind control helmets. Except for his evil minions. If any minion did disobey Kevin, then they would be made into one of Kevin's slaves as well, and this meant that none of his minions every disobeyed him. They were just as evil as he was and they liked being evil.
Nazz ran away from the cul de sac after refusing to marry Kevin. She did not want to marry an evil mastermind who had no sympathy whatsoever for others except for himself. She hid and after findng a book titled "telekineses for dummies" she began training herself to become a sith lord.
Gradually, she began gathering survivors who had also managed to avoid becoming Kevin's mindless slaves, and began training them to become siths as well. She hoped that one day she would gather an army large enough to defeat Kevin and bring peace and justice back to the world. She also wanted to free Eddy so she could go on a date with him.
Kevin devoted several soilders to seeking out Nazz and bringing her back to him. But they never found her.. Several years have passed since Kevin began his search.