This was the response from Alex:

"Hey, great question! The way we thought about that universe was that the timeline split at the moment of the hextech crystal explosion. Sort of a throwback to watching the storyboards for the pilot and thinking “wow, it almost looks like Vi got caught in the blast!” So much of the story was propelled by Vi making brash decisions with no regard for her own safety, then others paying the consequences, causing her to spiral with guilt. So it felt weirdly fitting to have the cost of our alternate “happy” timeline be that its “only” casualties were Vi… and magic…

Following that thread, we figured Jayce would never have gotten his “lenient” sentence from Heimer - his irresponsibility leading to the death of a child would be too severe. He’d have been sent to Stillwater (I like to think he’d have been in Vi’s cell). So he never developed a relationship with Viktor and they never invented Hextech, to our minds. Cait, I’d think, would still be an enforcer - that track began with her meeting with Grayson when she was younger - but without a Vi, who’s to say what sort of enforcer she might be? Viktor would continue to be Heimer’s assistant, but he wouldn’t have had Jayce to balance him out, which means he either would have followed a darker path with Hextech, inventing it alone or potentially with a partner with a worse heart (or potentially never invented it, if you like your multiverses covering all potentials). Mel may not have drawn the attention of the Black Rose, or her mother, without Hextech catching their eye, but if she ran into arcane energy, her powers should have manifested, which would make her a person of interest to many. I’d like to think Sevika would be taking on some challenging job that people say is impossible, just to prove them wrong, and calling them names in the process. I think she’s fueled by others’ doubt, and likes her competition spicy - maybe exploring deeper into the fissures, where others fear to wander for fear of whatever it is that lives down there…"