Piano strings do require replacing ! Depending on use a set of strings should last for 15 plus years. The bass strings loose their qualities first.. often cleaning the bass strings help but, eventually all do need replacing. They degrade very slowly and a player will not notice until it is long gone.

Replacing strings also requires replacing tuning pins.. and usually is associated with general refurbishing of the action, keys etc.

We are in the piano business and you can expect to pay in the range of $1K for a string job plus any other associated repairs and there usually are additional repairs required. The average piano has 256 strings so it is a labor intensive process but well worth it in the continued enjoyment of a fine instrument