It wouldn't be one single rappel. He would go from the top to an anchor point, reset his rope and then rappel down to the next anchor point. He would repeat this all the way down. Anchor points need to be approx half the length of his longest rope. That way he can retrieve his own rope and use it again and again.
On long rappels with limited anchor points they can tie multiple ropes together. They have no difficulty moving past the knots. On occasion a climber will mis-calculate and be forced to tie their rope from its end to an anchor point to make a long rappel. They make the rappel just fine, but are unable to retrieve their rope. It stays on the mountain. On rare occasions a climber will terribly mis-calculate and rappel off the end of their rope. As you would imagine this ends quite badly.
