Nominating anyone other than Clinton is handing the GOP the Presidency for at least 4 years.
That's good news for John McCain.
There is no indication that 2016 will be anything like 2008.
There's no indication another Democratic nominee would be weaker than Hillary once the campaign started. Not that it matters. If she runs, she'll be the nominee.
Back when people bothered to poll Biden, he did much worse than Hillary every time despite having similar name recognition. Of course, you can guess that Hillary will fall/whatever other Democrat will rise, but your guess is as good as anyone's on that front. I'd much rather be ahead at this stage than behind, even though things can change.
I cannot deny Hillary is a frontrunner and I won't be surprised if she's nominated, but things can indeed change. If every frontrunner at this point would have been nominated, we would have President Gary Hart or President Rudy Giuliani or President Clinton, finishing her second term.
The point is: Hillary's nomination is not a forgone conclusion yet and other Democrats lack of electability is not a forgone conclusion either.