Is the Republican Party truly in danger? I doubt it. The utter clusterf**k that is the US economy is pinned squarely on Obama now, rightly or wrongly (wrongly), and the GOP had a deathgrip on one of the two houses of Congress and can and have ground Democratic Presidents to a total halt in terms of agenda. None of this will change if Clinton wins in 2016, she will flounder as ineffectually as Obama has now that the GOP has realized that they can just...not pass anything.
The GOP's "deathgrip" on the House is vastly overstated. Supplant the 2006 or 2008 political environment into 2014 and the House flips easily, despite the gerrymandering.