say I need a reinstall but don't have the files anymore and just want a clean reinstall of FSopen, how do I extract the retail files from my current installation seeing I will need it?
You will only need to backup the following files:
root.vp
smarty_fs2.vp
sparky_fs2.vp
sparky_hi_fs2.vp
stu_fs2.vp
tango1_fs2.vp
tango2_fs2.vp
tango3_fs2.vp
warble_fs2.vp
Backup these, and build your new FS2_Open directory around these.
Basically, all you REALLY need to run FS2_Open (excluding additional content) is these retail files, a FS2_Open build and the Launcher in same directory. That gives you the basic installation, and from there the game will generate /data/* directories that it needs for storing pilot data etc. Then you just add mod directories for the community-made content like mediaVP's and campaigns and so forth.

Technically you don't even need the Launcher, but it's the easiest way to generate the necessary registry entries on Windows if you don't actually have the game installed.
EDIT: If you want to preserve your pilot files, you should also copy the /data/players/ directory.