History has shown many such betrayals--- there was the betrayal by Norman Thomas that led to the decimation of the Socialist Party; and, there was the betrayal of Earl Browder which led to the decimation of the Communist Party USA... both Thomas and Browder had built much larger and more powerful movements than Bernie Sanders has, but we shouldn't minimize what Bernie Sanders contributed because it has been important.
Bernie Sanders now joins the legacy of these betrayals--- those who built large and powerful movements only to take the wrong turn and destroy what they helped to create.
But, life--- just like the class struggle--- does go on and people will find their way to doing what needs to be done... with or without Bernie Sanders.