So what happens to Kerry's funds after the convention?

Kerry is still fundraising, the convention draws near, and he still has tens of millions of dollars in the bank.

So what happens to all this money?

Money spent on advertising at this point in the campaign has limited value.  He could repay his loan but that hands the Bushites a day of gloating.  He can't pre-pay expenses as some suggest (salary, advertising, etc.)

Does he hand the money to the DNC who can then spend it essentially (but not explicitly?) on getting Kerry elected?

How has this worked in the past?