Stan could be a likely hero. He's often the voice of reason in the show. He would probably be the one to come up with a practical plan to survive the zombie apocalypse, like finding a secure place to hide and stockpile supplies. He also has a strong moral compass which would help him make decisions about whether to help other survivors or not.
Kenny might be a hero in his own right. Since he has the unique ability to come back to life, he could be used as a sort of guinea pig to test different ways to defeat the zombies. He could sacrifice himself multiple times to gain knowledge about the zombies' weaknesses. And his rough upbringing might give him an edge in the harsh zombie - infested world.
Harry Potter himself would be a likely hero. He has already faced Voldemort and numerous other dark threats, so he has the courage and experience. His ability to think on his feet and his connection to the powerful Patronus charm could be very useful against the zombies.
Definitely Harry Potter himself. He has faced so many dark and dangerous things already, so he'd be able to handle zombies. Hermione would also be a likely survivor. Her vast knowledge of magic and quick thinking would serve her well. And Neville Longbottom. He has shown great courage and has a deep understanding of Herbology, which could be useful in creating defenses or finding antidotes.
The members of Team JNPR could also be likely survivors. Jaune has grown a lot in his skills. His leadership and swordsmanship could be useful. Pyrrha, if she were still alive in this fanfic scenario, would be a great asset with her combat abilities. Ren's calm and collected nature, along with his stealth and combat skills, would help him survive. And Nora, as mentioned before, would be a great addition to the group of survivors. They could work together with Team RWBY to face the zombie apocalypse.
Well, Kyle could be a strong contender. He's intelligent and has a strong sense of justice. He'd be able to strategize well and form good alliances. However, his temper might get in the way at times. Another possibility is Stan. He's fairly resourceful and has a good heart, which could help him gain allies, but he might be too hesitant to make tough decisions sometimes.
One idea could be that the kids of South Park form their own survival squad. Cartman might try to hoard all the food, leading to comical in - squad conflicts. Another could be that the zombies are actually the result of a failed experiment by Professor Chaos, and the boys have to find a way to reverse it. Maybe Stan and Kyle have different ideas on how to deal with the zombie threat, with Stan being more practical and Kyle more idealistic.
Obviously, Stan, Kyle, Cartman and Kenny are the most likely. They're always at the center of the action in South Park. Their different personalities would lead to really interesting time - travel scenarios. Stan's more level - headed nature might be the voice of reason during time - travel chaos. Cartman would probably be trying to use time travel to his own greedy advantage, like finding a way to hoard all the cheesepuffs in history.
Jude could be a likely hero. He's always been kind of a risk - taker and he might be brave enough to face the zombies head - on. His quick - thinking could help the group get out of tight situations.
Lex Luthor. He's always looking for a way to take down Superman, and an apocalypse would be the perfect time for him to make his move. He could be using the chaos to build some sort of doomsday device or manipulate events to his advantage.
Well, the heroes would have to adapt their powers. Uraraka could use her Zero Gravity to lift zombies and drop them from a height. Todoroki might freeze groups of zombies with his ice side. However, they'd also face challenges. The chaos of a zombie apocalypse could disrupt their normal teamwork. And they'd have to deal with the moral dilemma of killing what were once humans, which could be a huge psychological burden for the more empathetic heroes.
Toga might be interested in the zombies in a different way. Since she has a fascination with blood, she could study the zombies to see how their blood or 'undead' state works. However, other villains might just be in it for themselves. Dabi, for example, might just burn his way through the zombie hordes without much thought for a grand plan. He'd be more focused on his own survival and causing chaos.