They have already given up on the issue. The last time they used it as a wedge was in 2004 when Bush came out in support of Federal Marriage Amendment and the GOP got gay marriage bans on the ballot in 11 states (including Ohio which was a tipping point). But in 2012 when Obama came out in favor of it, the GOP accused him of "playing politics", essentially accusing him of pandering and using it as a wedge issue.
Moving forward the GOP will use opposition to gay marriage like they do with abortion, primarily as a fund-raising tool with their base but not something they overtly campaign on on presidential elections. Nominees will be against it, with the caveat that it should be left up to the states (and therefore not the SCOTUS, which is also their view on abortion).