However, by that time, Li Zhirui might no longer be in the Integration Realm.
Besides, even if he stepped in to help, it doesn't necessarily mean he could kill that Demon Cultivator. That's a Mahayana Demon Cultivator, capable of wielding countless life-preserving techniques. He might end up getting himself killed in the process.
Even if he somehow succeeded in killing him, the promise from Yang Wuquan of handing over all the Spiritual Objects seemed utterly unreliable to Li Zhirui.
Especially when it's just this kind of unbinding verbal agreement—after the deed, they might shamelessly deny everything, or worse, kill him to silence him. Li Zhirui was not strong enough to contend with that.
The best approach is exactly what he's doing now: ignoring and avoiding the situation altogether.
One must have a clear understanding of one's own strength, without overestimating oneself or imagining you can tackle every problem.