Going away? W won 44% of the Hispanic vote in 2004 and he still only won 50.7 to 48.3 in the popular vote and 286-251 in the electoral vote. And 2016 the Hispanic vote will be a larger percentage of the vote than in 2004.
We are in middle of a stretch that will last a third of a century if not more where no Republican will win POTUS "going away." The last time a Republican won POTUS "going away" WVU had never won 10 games in a season in football. If the GOP wins in 2016 it'll be by a small margin.
Hillary is an exceedingly weak candidate. She's a liar and a felon. Americans simply don't trust her. You're mistake is believing that nothing changes. Hearts and minds don't change. Blacks and Hispanics will forever provide Dems cover.
The problem with that is that changes do happen. Blacks are exceedingly poorly served by Dems. By almost every measure, Blacks are worse off today than in 1965. Poverty, single families, crime, drug use, incarceration are all higher.
Hispanics are very socially conservative. Hispanics also want jobs. Just as Reagan changed the minds of many Dems (Reagan Democrats), Rubio has that same opportunity.
Other constituencies have similar issues. Will unions support Dems that want to destroy energy jobs? Will unions support Dems that want to tax their health care policies and a President pushing "free trade"? Will unions support Dems that want to import cheap labor? Will Blacks, for that matter, want new, cheap labor to compete with them for jobs?
What a party is made up of so many constituencies that may have competing goals and ambitions, fractions are inevitable.