True. Many ancient cultures did not yet have a very complex set of beliefs concerning the afterlife. They believed that when we die, some part of our being goes to the realm of the dead, a place of darkness usually thought to be located beneath the earth (totally not a pleasant place to be in, of course!) and permanently stay there, cut off the land of the living, never to return - save for a few exceptions. Regardless of deeds or station in life, all humans, good or evil, are thought to go down the underworld. For the early Israelites, this was Sheol (the “Pit”); for the Greeks, this was Hades; for the Japanese, this was Yomi. We can find this earlier concept in the older parts of the Old Testament.
Since the Sadducees were somewhat doctrinally conservative, they probably would not have welcomed the more detailed conceptions of the afterlife that was gaining currency among Jews and thought of them as ‘innovations’. If anything (this is just speculation since we don’t know much about them), they would probably have still thought that our shades go to Sheol and forever dwell there. To be honest, though, Jewish eschatology today is still rather vague on a number of points (the concept of reward for the just is there, but the whole subject of damnation for the wicked is something that is uncertain); it is with us Christians that conceptions about the afterlife grew elaborate and specific.