From: the Netherlands
You have to rebuild the unit from "destroyed groups" tab. You will be able to use it again in a year. The fragment is just that, a fragment. If all planes are repaired and you disband the frames will go into pool, if they are damaged or in maintenance they will destroyed. You will recover all the pilots though.
in short - the fragments are worthless, disband them into pool or another unit. In a years time you will be able to use the unit again (IF you pay the PP)
Edited for my crap spelling and such
"It happened, therefore it can happen again: this is the core of what we have to say. It can happen, and it can happen everywhere.”
¯ Primo Levi, writer, holocaust survivo