There is no way it would be 'repealed'. A constiutional amendment can only be repealed by another constitutional amendment, and while opinion my shift more in favor, there will never be enough support for a constitutional amendment to allow gay marriages.
A recent NY Times poll showed, to the Editorial Board's chagrin, that well OVER half of Americans rejected the idea of homosexual marriage. A large majority also expressed opposition to homosexuality as a lifestyle. This was a total shock to the Old Grey Lady which has been trying mightily to change public opinion in this regard.
If now, after several years of homosexuals on tv shows, in the movies and the tabloids, Americans are STILL not accepting of the lifestyle, I don't think that time will ever come. In fact, the more often homosexuals are portrayed in the media, the less average Americans are accepting of them.
Only time will tell but, based upon my observations of todays teens and young adults, 90% of them view homosexuality as being normal and acceptable. Within a couple of generations they will be the majority. That majority coupled with homosexuals framing the debate of non-traditional marriage as a civil rights issue will provide strong support for the repeal of any Constitutional Amendment concerning marriage.