The vast majority of us who choose to be queer remain queer for the rest of our lives. Although a few "lesbians until graduation" or other ex-gays may have identified as queer by choice before changing their minds and trying to become heterosexual, the majority of such people do not seem to have ever wanted to be queer in the first place. The majority of these people also do not seem to have gotten very far in the process of coming out as queer before trying to re-establish themselves in heterosexual identities instead. It is generally safe to assume that those of us who have bothered to go through the considerable difficulty of trying to persuade friends and/or family members to accept us as queer would not have bothered to do this if we were planning to go through it all over again by trying to persuade the same people to accept us as heterosexual. It is also generally safe to assume that if we say we like being queer and we feel it was a good choice for us, then there is no reason we're likely to suddenly change our minds about those things in the future.
If you explore the QueerByChoice Mailing List Member Profiles or the Queer by Choice LiveJournal Community members' LiveJournals, you'll find that a large percentage of queer by choice people have been queer for many years and are in queer long-term relationships or marriages.
In addition to the fact that most queer by choice people have no desire to turn heterosexual, some of us also doubt whether it's even possible, after having already chosen to be queer, to choose to turn heterosexual instead. (See "Could you choose to turn heterosexual if you wanted to?" for more explanation.)