This happens frequently with my teacher's piano. For example, for a few of the notes in the lower register, one of the two strings have been broken.
The tuner has advised my teacher that in such a case, you should not simply replace the broken string with a new one: it won't work to have one old string next to a new string. So what my teacher is doing now is to wait until the other string breaks as well before doing anything about it. Unfortunately (or fortunately?), that other string is proving to be a lot more resilient.
My gut reaction in such a case is to replace the one that is not broken as well so you have all new strings for that note. However, my teacher seems happy to live with only having one functioning string. Can that be justified, or is he trying to save money?
If you are a technician, what would your advice be? If you are pianist, would you live with it? It just doesn't seem right, how you can make the same music when some of the notes don't have all the strings? To be fair, it's not easy to notice that some of the base notes have missing strings. Perhaps this is a testamount to how bad the piano is?