LOS ANGELES, Dec 12 (Reuters) - The sequel to movie box office champion "Avatar" arrives in theaters this week, 13 years after the first film, as cinemas try to recover from the pandemic and draw people away from streaming at home. Hollywood's big question about "Avatar: The Way of Water" is whether the follow-up to the highest-grossing movie of all time can attract enough moviegoers to recoup its massive production and marketing costs. Director James Cameron admits he is not sure. "Can we be profitable in a changed market? Or are we just the last dinosaur dying after the comet...