If there was no iCarly (God forbid!) and Carly, Sam, and Freddie never met... what do you think they would be like?
Carly: I think she'd be part of the gossip/popular crowd. Her best friend would be Missy or Wendy and she'd have some jock boyfriend who's all dumb but quite attractive. Without Sam, she'd be a prissy, spoiled little brat (please don't start a fight about how she already is. Face it, Carly does have at least SOME modesty and gratefulness.)
Sam: Sam would earn the reputation of the school bully/rebel, and would be kicked out of various schools many times because of it. She'd be held back a few grades and be in classes with people that are younger and that she can boss around and beat up. Throughout high school (assuming she gets that far) she would be in deep trouble from her anger issues and violence... maybe juvi or she'd get into drinks or drugs...
Freddie: He'd be a total nerd. In elementary/middle school he'd be constantly bullied and teased for his academic talents. He'd be completely vulnerable, as he did not take any sports or exercise at all, and becomes very weak. Without Sam to toughen him up a little, he'd always be a target for others.
Without each other, they're all a mess :P