After the truth of the world coming to an end became known to Sebastian, he could not help himself from thinking about the safety of those close to him.
Throughout his 8 months spent in Oceania, he had seen a lot of things but he only bonded deeply with 2 different groups which were Leroy and the members of his clan, and Old Mak and the old clan.
Leroy then was nothing but a half-baked orange tier predator, yet he was the strongest predator of the Leroy clan.
Old Mak's clan was better as Old Mak being the strongest predator and protector was a powerful purple tier predator, still yet, when faced against the bigger picture, Old Mak and Leroy were nothing more than cannon fodder.
When Sebastian learned of the misfortune that befell the Leroy clan, he was sad but this only verified his conjecture that Leroy and the others were cannon fodder. They were just too weak to influence the bigger picture.