Why not just update it?
And if the update doesn't work, or the PC becomes unstable, or whatever then what? Giant hassle of re-installing Windows 7 from scratch to get back to where it is now, and I still have the problem of how to avoid Windows 10. Or are you living in dreamland and assuming a 100.0% success rate with every automated upgrade? I have no experience with Windows 10 and while it might be similar it isn't identical so when they do have problems it will waste more of my time trying to figure out how to fix them.
Why should my parents and me go through ANY additional hassle and take even the SMALLEST risk of problems just because Microsoft wants to get them aboard the data collection machine known as Windows 10? Windows 10 provides them exactly ZERO benefit and will not improve their PC usage experience in any way whatsoever. What's in it for them?
If the manufacturer of your car decided they wanted you to bring your car in for service and leave it for the entire week so they could replace the engine with one they assured you was identical, but might not be quite identical, and would collect metrics about how many rpms it was at during different times of the day or whatever, would you simply do it because they say so? Not talking about a recall, since it isn't a safety issue or fixing something that is broken, it was just because they wanted to and there were no guaranteed benefits over the engine you have now other than your warranty that now runs until 2020 would be extended a bit. I think you would say "my engine works perfectly fine now and I see no reason to inconvenience myself by bringing it in, and risking that maybe my mileage will not be as good and possibly waste time getting used to different noises it makes from the ones it makes now, and the data collection thing is not for my benefit"