Alex decided to not lodge a complaint about what happened for his own sake. But what was keeping the people that had poisoned him from doing so?
Right now, at the very least, 2 people were aware of the fact that he had in fact survived a poison that was far beyond his capacity to survive.
An act of revenge on the First Elder's part had revealed the fact that he could in fact survive such a dangerous poison to not only the First Elder but also the Elder that had partaken in his murder.
Two people in the sect were aware of very important information.
Fortunately, Alex didn't believe they knew he could survive such a strong poison. If he was in their place, he would believe that he had cheated somehow. Maybe a pill that he ate beforehand to deal with the poison.
He was an Alchemist after all. Making a pill that preemptively attacked poisons was not an impossibility on his end. God knew the woman thought he could do way more than just that.