They serve very different purposes, so many photographers would keep both.

The 16-300mm is a superzoom: one lens that covers wide-angle to strong telephoto. It’s convenient when you want flexibility, such as travel, walkaround use, or subjects at changing distances. At 16mm it shows a wide view; at 300mm it narrows the view to bring distant subjects closer.

The 50mm f/1.8 is a prime lens: fixed focal length, but with a much wider maximum aperture. That wider aperture helps in lower light and makes it easier to get a blurred background for portraits. It’s often considered a “normal” or portrait-style lens, depending on your camera.

Tradeoffs: superzooms are convenient but typically slower and may not match a good prime for low-light use or background blur. The 50mm is less flexible in framing because you must move your feet instead of zooming.

So: use the 16-300mm when versatility matters; use the 50mm when you want better low-light ability, shallower depth of field, or generally stronger image quality from a simple lens design.