I kept him alive. Mostly because of what Lucien Lachance said. Great respect for that man, and he said that he thought Sithis would want Cicero alive.
Also, he really is the only TRUE Dark Brotherhood figure still around. He follows the 5 Tenents, which Astrid abandoned, and he cares about the Night Mother.
Also, not only will he be a companion, but he treats you like a f**king rockstar whenever you walk into the Dawnstar Sanctuary if you keep him alive

. Also helps to make the sanctuary feel a bit more lived in.
You can still get cool Jester clothes I believe. He's a psychotic freak who attacked Astrid but still... Astrid wasn't exactly being a true Dark Brotherhood leader. Cicero was acting in the name of the true leader.