I have a piano in my mom's place. It is not that old but I remember the guidelines that the piano tuner gave to us - a constant humidity etc. Strings is (as for me, I might be wrong) is the part that is easiest to replace.

BTW, I just recalled a story that happened in an oldest Kyiv pharmacy-museum. I was there with a small tour. It is in a former house of the pharmacist and there is an old piano there. The director of the museum shared a story about the piano keys made of ivory. After another excursion, he discovered that someone had stolen one of the keys. (WHY??) It was replaced just before my visit. One of the excursionists played the piano well, and he let her play! It was the first time in nearly 200 years that anyone had played that piano. Incredible story!