Romney did not lose in 2012 because of immigration or Hispanics. It might have been closer, but Hispanics had nothing to do with Romney losing OH, IA, NH and Wisconsin and Romney needed at least one of those (OH) even with VA, FL and CO where minority voting had an impact.
Romney would have lost amongst Hispanics anyway for the same reason he lost overall because he offered nothing that could promise a better outcome for low income working and middle class voters. No healthcare alternative, nothing stubstantive on education, didn't endorse minimum wage hike until over a year afterwards and so forth.
Mitt Romney actually did better with whites than Bush Jr. (59% vs 58%). So Romney's loss is entirely down to his extremely poor performance with non-whites. Romney 'self-deportation' and hard anti-immigration positions in the primaries (along with others in the party) were definitely a factor.
The 2013 GOP autopsy noted that the party lost because of how poorly it did with the 'Obama coalition' and mostly talked about communicating better with young voters, women, LGBT and minorities. But there was only one single policy position it endorsed: comprehensive immigration reform.
The math is simple. If the rise in the non-white % continues into 2016 and if the GOP gets the same 18% as the last two elections, they will need 64% of the remaining white vote to win, something they have only done once in the last 10 elections (Reagan 84).
