I was thinking on the bus today after a hard day of inventory when I thought of that poor dwarf bookkeeper who must count all 924,512 pieces of stone to absolute accuracy, simply because the overseer told him to. Whats more, he must do it alone. Sure if he finishes he will be the greatest counter in the entire fortress, but if he dies there is the chance that no one will have any bookkeeping skill to replace him with.
My idea,
Have a deputy for all noble positions that helps the primary with his work, works opposite shifts as the primary, and acts as a successor to the primary should he die. By working with the primary, the deputy is able to build experience in the exact same skills as the primary, thus insuring the replacement is at least competent.
Assistants could be added to each noble (with more important nobles having more assistants), whose job it is to keep their noble fed, clean and happy during their work hours. If a bookkeeper is thirsty while working, the assistant will either grab some alcohol from a flask, or go to the kitchen for some. The assistant will learn some skills as they help their noble with their work, thus providing another alternative in case both the noble and the deputy are killed at the same time. It also means that the noble has no excuse to walk off during their shift for a drink.
Some Ideas:
The army will have the captain (the noble), who commands the entire army of a fortress; a lieutenant (the deputy), who looks after the sergeants during the captain's off duty hours and is second in command; the sergeants (noble, below the captain/lieutenant) are in charge of their squads and look after their charges training and schedule; the dwarves in a squad would take over the position of sergeant if the sergeant dies, based on their position in the squad.
Both the captain and the lieutenant would have a batman (assistant) who looks after the cleaning, cooking, weapon/armour maintenance, paperwork and security of their noble. If the captain does not feel like putting up their field tent, the batman does it instead.