It is often more sensible to repair something than to replace it completely. Helping the customer weigh their options is an essential part of my business.
You'd be surprised at what can be repaired, rather than replaced (Always save the pieces!). For example, I often repair old windows by replacing rotted sills or other components. Sometimes a customer will want to replace their windows outright; other times, this is neither desirable, or cost effective. It is often more economical, even when the components are quite customized, as with the window below. I replaced the top half round sash which had completely rotted at the bottom joints:
There is often little point in replacing an entire system when only one or two components are faulty.
It is usually cheaper and less disruptive to repair plaster than to gut a room, unless there are compelling reasons to do so, such as massive adhesion problems, disintegration, etc. Plaster, if it was competently installed in the first place, will outlast most of the drywall installed in the past half century.
Repaired and reinforced plaster curves with a new abutting sheetrock wall:
Almost anything can be repaired! As time allows, I will update this page with more examples.