http://www.slate.com/id/2190880/*snip*
What happens to all that debt when she drops out or the election's over?
It needs to be paid back—unless the candidate is the one owed the money. Lenders want their money back, and they are expected to follow the same practices they would if they were lending to a business or an individual. (If Clinton had borrowed from a bank, for example, she would be required to pay interest on the loans.) Moreover, under campaign finance law, an uncollected loan from a corporation—whether it's a bank or a sign maker—could be construed as an illegal contribution. As a result, even though vendors don't always require campaigns to pay upfront, they must make a good-faith effort to collect on any money they might be owed.
Debt retirement gets a little more complicated when candidates lend their own money to their campaign. After an election is over, any campaign contributions that go toward repaying the candidate's own loans serve, in practice, as money directly into a politician's pocket.
As a result, campaign law (PDF) now limits to $250,000 the amount a campaign committee can repay the candidate after the election. In the case of the Democratic primary, the election will end when a nominee is selected in Denver.
So unless Clinton is able to raise enough money to pay herself back by then, she'll have to write off millions of dollars she lent to her campaign.*snip*