Items do despawn if they're not in the range of a workbench. The time required seems to be a bit fuzzy. Sometimes it's the next time you go to sleep, sometimes it takes a few days, sometimes more. It may have to do with how the game loads/suspend areas of the world. But anyways, the details are not important I guess, to answer your question yes things will eventually go away as long as you don't throw them on the ground in your base.