Music changes but hopefully his sound will influence others. Although it won't sound like Truck's southern rock drumming, maybe it won't disappear since it will provide musical inspiration for someone else. In any case, as long as you can hear the music, it won't really be gone or forgotten, it just might not be often heard.
While Buthch Trucks was an amazing drummer, and he will leave behind a big whole that is hard to fill, Butch Trucks is not the last great Southern Rock drummer. There are other Southern Rock bands that have great drummers and are up and coming. These bands are the next generation of Southern Rock.
Where there is someone who does something well, there is always someone who will come along to emulate what that person did. Even though Butch Trucks was a big name in Southern rock drumming, it is a genre. That means that there are others who do it and other people who appreciate it.
The Allman brothers band, including Butch Trucks, were the pioneers in southern rock. They paved the way for many acts that are popular today. Many current country music acts mimic Trucks sound. His passing marks a legacy of culture that thrived for the past three decades and will continue to do so in the future.