I struggled with the lilac root system for 4 years when I bought an old house. Lilac roots spread horizontally and produce a lot of shoots.
But 4 years later, in the spring, I saw that 3 lilac trees simply weren't covered with leaves and literally fell down - their roots had rotted away. And all the shoots had disappeared. What was that? I don't know. But since then, lilac has not prevented me from living, it has disappeared.