I'm not sure I understand the complaint that the Twilight series is "heteronormative" or celebrates abstinence. Almost by definition, a romance featuring a heterosexual man and woman presents a heterosexual relationship in a positive light. This is true not just for Twilight but also for Brides Maids and Captain America, and few complained that those movies "reinforced" a heterosexual norm. It is possible for a movie or a book to tell a story about a romance without suggesting that others' romances are unworthy. I don't see how Twilight's love triangle oppresses others' loves.
It seems to be a recurring theme in literary (and even cinematic) criticism that works focusing on disadvantaged groups of every stripe are inherently more worthy because they come weighted with the academy's fetish for narratives of oppression. Instead, Ann Rice probably had it right when she told the Daily Beast that Twilight was simply an old Gothic romance dressed in new clothes:
What I say right away is they take the formula of women’s romance that was used by Jane Eyre, and they put it in a new context. You have the young girl, Bella; she falls in love with this mysterious figure, and he’s menacing just like Mr. Rochester was in Jane Eyre, but he’s protective. I think it’s an enduring formula.
There is a lot to criticize in Twilight (especially the godawful wretchedness of the prose, seemingly innocent of any editor's blue pen), but I don't think the fact that the characters are engaged in heterosexual romance leading toward traditional marriage is one of them. There are only so many permutations of gender possible in a binary relationship, and sometimes heterosexual coupling is going to occur. It's not as though the vampire genre lacks alternatives; as far back as 1872 J. Sheridan LeFanu offered a lesbian vampire in "Carmilla."
Below is the original illustration by D. H. Friston from the first printing of "Carmilla." The angry man with the phallic sword is trying to stop the lesbian vampire from molesting a passive girl's heaving bosom in bed. Hmm... maybe there's something to this heteronormative stuff after all...