I guess it's fair to ask how Hillary would have done in a wide open race where there were a full stable of Democratic candidates for President in 2016. How would the thing have played out of Hillary didn't have DWS clearing the decks for her at the DNC, and she went up against a field of, say, VP Joe Biden, Sen. Bernie Sanders, Gov. Martin O'Malley, former Gov. Deval Patrick, former Sen. Jim Webb, Sen. Sherrod Brown, and a few other challengers. Would she have still won the nomination? Indeed, if the decks hadn't been cleared, I think O'Malley (for example) would have done better.
DWS and the DNC aren't that powerful. The decks weren't cleared by them. They were cleared by party elites (including elected officials and the like) and big money donors, not the DNC itself. These folks basically signalled to Cuomo, Klobuchar, Patrick, etc. that they were going to back Clinton, and so there was no space for a non-Clinton establishment candidate in the race. It's similar to what happened with Romney in 2015, where the big $ donors and other elites who he was hoping would back another run by him ended up migrating to Jeb Bush, leaving no space for a Romney candidacy. That was something that happened because of the party elite, not the actual RNC.
So I'm not sure exactly what you mean in your hypothetical about the decks not being cleared. If the question is "What would have happened if the 200 or so Congressional Dems and a couple of dozen governors hadn't all endorsed Clinton early on, or if her Super PAC backers hadn't backed her, and had instead spread their money around to folks like Cuomo and Biden?", then I think the answer is that Sanders would very likely have won a plurality of the vote, because the "establishment lane" would have been split, while the "insurgent lane" would have all been Sanders.
