Never is a long time. Assuming that humanity survives long enough there is no question that some day in the far off future it will be safe to return. Its probably just as likely that before never some technological breakthrough, maybe in nanotechnology, will come up with a way to clean up the radiation.
No, it will never be safe for humans to live near the site of the catastrophic nuclear accident that happened in Chernobyl. While scientists may deem that the area is safe many years down the road, I would not allow myself or anyone I cared about to live near Chernobyl.
The Shelter was erected in a short period under conditions of severe radiation exposure to personnel. Measures taken to save construction time and to reduce the high dose rates inside the structure led to imperfections in the Shelter as well as to lack of comprehensive data on the stability of the damaged Unit 4 structures. In addition, structural elements of the Shelter have degraded due to moisture-induced corrosion during the nearly two decades since it was erected. The main potential hazard of the Shelter is a possible collapse of its top structures and release of radioactive dust into the environment.
I do not believe it will ever be safe to move back to Chernobyl. While there are residents that moved back to Chernobyl and are currently living relatively normal lives there, this is not to say that they doing so among the radiation that still exists. Every person is different as far as chemical makeup goes so the speed at which the radiation will affect them is dependent upon that. The current residents could be overwhelmed by the radiation shortly after moving back or could live a several years, depending on how their bodies handle and fight the radiation. The half-life of radiation varies largely, but all the half-lives are longer than a human life-span.