In reply to Imedio:
With the appropriate gear and skills you simply abseil from the top in two parts.
If you know what you are doing you can leave no gear but it is generally quicker, easier and safer to leave at least a maillon - a lot of the time you can recover whatever you leave from the next route.
Chances are there is in situ gear (or lower offs) in these circumstances but don't bank on it.
If you don't know how to do this (and given you are asking this question then it seems quite likely) get someone to show you, it's not a good idea to find yourself out of safe reach of the ground without knowing what you're doing.
Don't forget to knot the end of your ropes when abseiling like this (and when climbing). Be especially careful about doing this if you don't end up at the top - habit leads to lowering off and this can be dangerous if you're >1/2 rope off the ground.
Don't get complacent if the rope was "long enough" on the previous route or for the previous climber.