My guess is that this time, the big-money Democratic donors will be more willing to hedge their bets with multiple establishment candidates rather than be stuck in a 2016-style situation where the only alternative to the lone, ethically challenged establishment candidate was a radical outsider like Bernie Sanders.
The result of all of this is that Clinton, if she runs, will face younger and hungrier Democratic competitors while having weaker institutional and financial support than in the 2016 cycle.
She could still make a go of it, but it would probably be much more difficult to win the nomination, and she would risk embarrassing herself. It is bad enough that she is the woman who lost to Trump. The 2020 cycle will likely include several female Democratic candidates not named Clinton. Imagine if Hillary also became the woman who lost to the woman who really broke the presidential glass ceiling.