Could readers view the final scene in which Romeo and Juliet both die as triumph? Why?

No, I think one of the bigger themes in the novel is the two family's feud cost the lives of their children. R & J's love does not triumph because they are dead at the end of the play: there is only tragedy, this play is a Tragedy, and sorrow. Ironically it would seem that their deaths might end the family's endless fighting but we do not find out for sure.