Future potential candidates is one of the reasons that this election is hardly the doomsday scenario for the Republicans that some are making it out to be. The Democrats have four years to work on it, but right now the Republicans have a much stronger group of up and comers.
The GOP has a lot of problems but they are not catastrophic, the party needs to make some changes, as far as 2016 is concerned, the question is whether or not they can make them by then or need another election loss or two as encouragement.
If its internal power brokers play this smart they can turn a short term loss into long term improvements. Even had Romney won changing demographics would still be a big problem for them. With the loss they may be more encouraged to make some changes sooner than later. Big government social conservatism has tipped to the point of being a loser in a national election and will continue to become a bigger and bigger loser as older generations die off. Small government and fiscal responsibility can still get votes. They need to embrace and promote their up and comers who promote those views and sideline the social conservative aspects of their platform. For example, it is only a matter of time before gay marriage is legal throughout the country. Younger voters tend to be for it or indifferent about it, opposing it will hurt more and more as they replace the aging crotchety Christian conservatives the Republicans got in bed with. Likewise, abortion will increasingly harm them and presidents can't overturn the Supreme Court anyway so they will continue to have less and less reason to be outspoken about it. Which isn't to say they have to embrace things like gay marriage, they just have to stop being actively against it.
While it seems unlikely they will do it, the short-term smart move for them is to accept a repeal of the Bush tax cut on the the top income bracket and then dig in their heals on any attempts to raise the capital gains tax and/or corporate tax rate. They can make a stronger economic argument about not raising those taxes, look somewhat willing to compromise and limit the effectiveness of criticism about them being the party of the rich. Then they need to embrace some sort of immigration reform that will appeal to Hispanic voters. Their hillbilly constituents might not like it but the GOP needs to spread its brand amongst more non-white males.
Then they need their crop of up and comers to become very visible via press conferences, news show interviews etc hammering away at the fiscal irresponsibility of Washington while not saying a peep about social conservative issues. They should also make sure that non-white male party members like Susana Martinez are included in this. It may be cynical to feature them in such a manner but would be far less obvious than inviting them for token appearances at conventions and they need to make clear that a platform about smaller government and fiscal responsibility is not a white person (and white male in particular) platform.
The party is going to get shaken up some in the coming years, the question is how quickly relatively new faces like Christie, Rubio and Martinez can take control. It was the old guard that embraced the more divisive messages of the party, if they get to control another election they will lose then too, if the up and comers take over they will be more pragmatic as a collective group at least about this. Another thing to consider is that the various monied entities that bankroll the GOP will get sick of financing losing campaigns if it continues. If the Republicans are really owned by corporations as is often alleged they would be wise to put pressure on the GOP to open the tent up and drop the divisive socially conservative rhetoric.
But, of course, the 2016 election will largely be about Obama's second term regardless of if it is fair to the candidates or not. If the economy is doing very well it may not matter what they do and if the economy is still performing poorly the electorate will probably be tired of hearing about how it is all Bush's fault.