Hard drives arae cheap nowadays, I always keep a spare, just in case. Depends how good you are at backing up. I "share" my PC with my business, so everything gets backed up regularly. I've had at least four hard drives fail over the last 20 years, the first one failed within three months of purchase. They always fail when you're using them - like light bulbs!
They're easy to replace, takes about 10 minutes, but restoring the progs and data takes a lot longer.