Mari is NOT surviving for long πππ my girl is either dying of exhaustion, starvation, sacrificing, tricked or pure stupidity ππ₯she MIGHT survive longer in a group though, she could get them all killed though so id say a week or 2 solo and at least half a month grouped.
Kel, while being quite short would be smart and clever enough to survive at least a month alone. He'd help a team a lot too due to his knowledge from all-nighters. Then again, his stress levels would go up either causing them to do something reckless or be too tired to fight a zombie so i'd say a few months at the very least.
Elias is.. well it depends on the step honestly. 1-2 he is DEAD on day 2 but if it's step 3-4 he's learning in medical school and so would know how to heal himself and others. While this might not help solo, it would make him more wanted due to his expertise and would be protected more aswell. I can even imagine him finding a cure and having his teamates distribute it.