When is a reserve ship no longer worth keeping?

At what point is an old ship no longer worth keeping in reserve?

Scrap it when useful hull life is gone or the cost of making it viable for a defined role is unreasonable, while also matching reserve numbers to realistic crews and support.

A worn patch of hull or outdated software does not by itself make a ship useless if repairs and upgrades can keep it viable for an assigned role. The governing standard is adequacy for that role rather than equality with the newest frontline combatant. The fleet should retain the best ships it can actually crew and support, not accumulate hulls without a plan. Simpler escorts and patrol vessels may age particularly well because their useful functions depend less on cutting-edge systems.