They all have at different points wondered how life with would have been different if Lyoko had never existed. What they don't know is that even in a world where Lyoko never existed they would met each other and be friends, to an extent.
In a way it starts because Aelita chooses to be a teacher and her quest to help the children of Kadic. This in turn is the reason she is Ulrich's favorite teacher because she helped discover he was dyslexic, and when his father tried to brush it off. Aelita smiled at him and told him she wanted to talk just his parents a couple of minutes. Ulrich is never quit sure what was said but when his parents exit his mother smiling and her eyes are laughing and his father right eye is twitching.
The end is result is Ulrich is more confident about himself, his parents are supportive, and his dad is not as hard on him and to Ulrich's amusement twitches at the color pink. However Ulrich is still a lone wolf.
In a more direct way the friendship starts with Odd becoming Ulrich's roommate. Though at first there is nothing friendly about their relationship. After three days Ulrich is ready to tell Principle Delmas about Kiwi because the dog keeps ruining his stuff and won't let him sleep and Odd dives toward him when Ulrich goes towards the door. Ulrich pushes back and this leads to a fight that their neighboring students hear. By the time Jim and Aelita comes to break up the fight Kiwi had hidden under Odd's bed, Odd has a back eye, Ulrich has a split lip and their laughing like old friends.
To Jeremy's horror Aelita spots him in the hallway and decides that he as a mature student, should hang out with Ulrich and Odd to prevent any fights and phases it in such a way that Jeremy doesn't want to disappoint her. It doesn't stop from him being annoyed at what he considers her diabolical plan to make him socialize, and the horror in his eyes still shows because Ulrich and Odd laugh harder. Aelita herself has to hold back a giggle in and Jim looks like he wants to strangle them all.
Yumi is next to join the group because she's heard about the fight and wants to meet the guy who gave her sparring partner a split lip. Over time the four become friends and in some cases more, though if asked Jeremy would say he could do without Odd complaining when Ulrich and Yumi get lost in each others eyes too often for his liking. Eventually William transfers to Kadic and hits on Yumi even after learning she's spoken for. This in turn leads to Odd and Ulrich pranking him, and ends that creating a prank war that only lasts a week before Yumi gets annoyed and beats them all up for being idiots. Somewhere along the way William becomes a friend and while Aelita crosses the line between friend/teacher, like Jim does, she's not really apart of the group.
The Lyoko group at different points wondered what life would be like if Lyoko never existed. Suffice to say if they could see it, they would be surprised at what would change and what would remain the same.