John G. answered 11/02/19
UC Berkeley Grad / Former Teacher / Masters of Education
Even though a plant may seem completely dead. Parts of it may stay alive (or at least dormant).
Annual plans only live for a year, so they make seeds that will scatter and grow into new plants the following year. Perennial plants stay alive through the winter - and might still die anytime if the conditions aren't right. They can make new plants from their root systems, broken parts, or even branches growing new roots into the ground.
By replicating themselves, there will be a higher chance that some of the plants will survive threatening situations like drought, weather changes, and diseases.