What happens when a Contractor fails to pay their remuneration?
Although this payment can be delayed, especially in the midst of
  combat, it is ultimately unavoidable. It is unknown what happens to a
  Contractor that fails to pay his obeisance, although Amagiri has
  stated that Contractors who fail to do so seemingly 'melt like butter'
  when depriving a captured November 11 of his remuneration.


Taken from: http://darkerthanblack.wikia.com/wiki/Obeisance

(It was also a pretty easy google search)