My comment wasn't to imply the only thing Clinton has going for her is her gay marriage position or that is her only position, merely that by settling the gay marriage issue the GOP would have a way to subtly move their way out of a controversial hot button issue that younger generations are overwhelmingly in support of. Liberal Catholics like Ted Kennedy did something similar when Roe V. Wade was handed down IIRC. Because frankly, right now the standard Democratic talking point seems to overwhelmingly be "WE ARE SOCIAL LIBERALS!", a point that would look incredibly weak if the GOP just moved on from this issue and ran on IT'S THE ECONOMY STUPID or something to that effect.
I would say that the fight is far from over. There are still 29 states without laws prohibiting discrimination on account of sexual orientation. In other words, while marriage equality is now legal in all 50 states, in 29 of those states you can be fired just for being LGBT. I think something like that leaves a huge opening for the Democratic nominee and something that I think the general American public will find quite unjust. Bills such as ENDA (at the federal level) far out-poll marriage. The American public will not accept outright and wholesale discrimination against LGBT individuals, which absolutely includes the workplace. If Hillary is to make this a top issue, she has to come out in full force and rail against the fact that it is still legal to fire someone for being gay. The marriage issue may be over, but gay rights are not. There is still work to be done.
