At least in the way that George and Lennie have seen the dream, it is dead.  There is no way that they are ever going to have that ranch now.

The reason for that is that Lennie cannot possible get away with what he has done.  He has not really murdered her, but no one is going to believe that it was an accident.  He is likely to be arrested, convicted, and at least put in jail for a long time.

So given that, the dream is dead.  Lennie is going to be killed or put in prison.  If George wants to continue with the dream, he needs a new sidekick.