Jeff, I think that playing Ennis was an important element of Heath's mission, and, Oscar aside, he more than fulfilled that duty. Hollywood will never be the same, those who made the film were touched by it and transformed, as have hundreds of thousands - millions? of others, since its release in 2005. We are still talking about it every day.
I think there are other parts to his mission as well, ones we may see begin to take form in reaction to his death. First of all, a renewed interest in his career, several of which were of deep social relevance. Another may be the increased daring of filmmakers to tread on formerly forbidden ground, and a greater willingness of the film industry to accept and to produce scripts that portray the struggle for LGBT civil rights. I think that his portrayal of Ennis also allowed an untold number of others to begin to pen their own tales, encouraged by the heightened awareness caused by the film. It is difficult to estimate the breakthrough this film has made - and the arts, particularly in the US, will never be the same.
The struggles of the LGBT population cannot remain marginalized in the "queer media." They must be made mainstream. "Will and Grace" and other popular shows in the media depicting gays, are effeminate caricatures, like African Americans in blackface or Jewish comedians in vaudeville. There had to be a first breakthrough to the mainstream, and Heath was part of the charge out of the celluloid closet.