Cat 5 is a write off I seem to remember. I wont guess at the rest but seem to remember something like repairable at unit level, maintenance units etc...
Cat. 1 Undamaged
Cat. 2 Capable of being repaired on site by the operating unit
Cat.3 The repair is beyond unit capacity.
Cat.4 Repair on site is not possible; the aircraft must be dismantled and sent to a repair facility.
Cat.5 Write-Off