Had Clinton not run, who would have been on the DNC bench?

This is more hypothetical, since it's been known for years that Hillary Clinton would be seeking the party's nomination in 2016. But it does bear asking, had she not been seen as so inevitable, or had the backing of most of the party's machine, who would have emerged as potential candidates?

1) Sanders -- He was likely in no matter what. His message is unique, and Elizabeth Warren would be the only other candidate to rival his message.

2) Cuomo -- From New York, but hated by liberals in New York. Would have received a well-justified Lieberman treatment.

3) Gillibrand -- Also from New York, a female, and ambitious enough to run for president.

4) Warren -- Maybe she runs if not for Clinton's perceived strength.

I support Sanders and his message, but something troubles me about the lack of youth in upper-levels of the Democratic Party. For a Party so popular with younger voters, it seems like O'Malley is the only fresh voice in the party. I like Castro of Texas, but was turned off with his characterization of Sanders as anti-Hispanic.