My understanding is we can stop when we have done what the Christ did.. to overcome all things including death. Once we learn to control our passions, and thoughts and actions and make the kind of choices the Christ made.. essentially.. by following his example.. then we get to the point we are given the power over death.. or having to re-incarnate. Of course.. we all have free agency not to incarnate again but then our growth or progression is damned.. or stopped.