"1 reformat and install the Linux distro of their choice. Or, if they're up to additional work, BSD." Just how I, as an average computer user who spends most of his time in MS Office and a web browser, want to spent a Sunday afternoon.
The average Linux install takes me about 40 mins - on a clapped out old Core 2. BSD can be installed in under 20 mins in most cases.
The problem with BSD is more the learning curve to admin it. However, admin is also the main problem with Linux. Joe User cannot do the admin role. But he can't do it for Windows either.
In reality, some other family member does it, and, increasingly, there are family members who realise it is far easier to admin someone else's Linux machine than someone else's Windows machine. Massively easier.
In the end, that will be what kills Windows.