Hmmm... Not big enough (and / or fast enough) to “destroy Earth”, but, Bennu could certainly remove most of human civilization (and numbers).
From the images, it looks like Bennu is basically a big pile of rock and gravel, rounded by gravity into almost a sphere, but probably not very cohesive at all. That might make it rather easy to blast into small pieces, 99% NOT in an Earth intercept course afterward, when it is still months away. OTOH, in a close pass by situation, it looks like it would not take much of an impact or interaction with some small object to knock off a chunk, said chunk then possibly* headed to Earth, with not much warning time.
*The odds of that are quite low, but 1/10 of Bennu would still have the potential to make quite a bang if it impacted Earth...
Similarly, an attempt to “push” Bennu, such as with a near miss warhead, would have to be done carefully, to not break it apart in an undesired manner...