info on roots please
 

If I remember correctly, epiphytic root is made of 2 main components, the velamen witch is the spongy grey/white matter, and the root itself witch is the hard cord-like structure in the middle.

My question is the following: if u have a healthy root except for half an inch section in the middle of its length witch is rotted and the velamen removed on that section,
are the nutrients picked up by the velamen away from that section still transported and used by the orchid?:hmm

The only section of the root that will remain in the long run is the section of healthy, undamaged, living root closest to the plant itself. The rest of it will eventually die off.

However, if all of the root is still alive, but there's a section that may be thinner than the rest - no matter where it is along the length of the root, it'll still grow.

Sometimes, the roots will branch (depending on the type of orchid you have).

I agree with Philip that the lower section will eventually die off. Whether or not I remove the lower section when repotting depends on the over all root health. If there is a lot of good root on the Phal I will remove the section below the break, but if it is short of roots I will leave it as I believe that for a while at least it will still work giving time for new roots or branches to grow.