If you use it just for Internet browsing and some word processing, there will not be much harm. If you keep your investments and checkbook on the machine, it might be more serious, but not necessarily critical. The software is easy to reinstall, and backed up data is generally safe. Some of my readers keep most of their data on floppy diskettes. I would much prefer to see it on the hard disk AND diskettes.
Playful pets love diskettes.
They have a predilection for the most important ones. What I am promoting here is the concept to be mentally prepared. That way you will never be blind-sided. It is rarely that bad. If the caller uses his computer for business, planning for failure is very important.