Should have worded my post better - what I meant to say was that in the view of some NO PARTS SHOULD BE REPLACED, even if this means the equipment will never operate again which, as someone else pointed out is not how the real world works. If you build a new boiler you section the old one to show how it works or store it or whatever.. Parts wear out etc.
Having said that one line over here has restored a 2-6-2T as a 2-6-0 "might have been" tender engine as the enhanced coal and water capacities suited their line better. There is, however, nothing to stop this loco being reconverted back to a 2-6-2T at a later date, which is what would have happened in the real world.
G