Nothing short of a resounding primary defeat in a major state in which she's strongly positioned is going to make Clinton drop out. But a few hundred thousand emails from committed Democrats letting the campaign know the extent to which her tactics are disaffecting large swaths of the party base and destroying her own standing might might inhibit the earth-scorching a bit.
A sample response:
To: Geoff Garin
From: A former Hillary supporter:
Since late March, Hillary Clinton's role in advancing the Democratic agenda has been entirely negative. She has been relentlessly undermining the likely nominee, violating Ronald Reagan's 11th Commandment and shredding her own credibility in the process. Her relentless flattery of McCain, her baseless claims to have crossed some mythical commander-in-chief threshold and her desperate willingness to seize on any minor gaffe of Obama's disqualify her to be the party's nominee.
If Ms. Clinton continues working to undermine Obama's core credibility as a candidate, she will permanently destroy her own standing and leadership stature within the party.