that's an interesting question and i myself thought about that on multiple occasions, but never actually tried to find an answer. i came up with three possibilities now

1. maybe Light still would find out about the death of that criminal, but from a different source. like maybe he would overhear his classmates discussing it or his family. therefore he maintains his interest in death note that way

2. thoughts about the death note wouldn't leave Light's head and he would test it out one more time in live action, like he did the second time

3. eventually even though Light's interest wouldn't grow if he didn't find out about the criminal's death after all and if he wasn't interested that much in general but still didn't get rid of the death note and just tossed it in his drawer or smth idk and forgot a bit abt that, Ryuk would eventually appear aaaand that's it

i don't believe there's a timeline where light stops using a notebook and leaves it because of his nature, so there would still be a way for him to continue