It didn't have to end early. When the manga ended I had my own narrative of how the show could continue. Do not keep reading if you don't want *spoilers*.
Yushiro, a demon who continues living, is eventually figured out by an occult elitest, who of course wants Muzan's power. Yushiro is cornered by him with wisteria and has his blood taken and absorbed by his attacker.
Death and Gang violence escalate in a modern world and Yushiro collects ancestors or reincartions of the Demon Slayer Core in order to fix what his existence has started.
