First, when Microsoft ends support for XP, will they also end support for XP Mode
Seeming that having a license for XP was never a requirement to use XP mode, I'm not sure where you're trying to lead this question...
as in create a patch that disables it?
The only thing that's ever been done with has been with MS's JVM back in the beginning of XP and it took a court to tell them to do that...
(I know he purpose of XP Mode was mainly so that people can migrate their systems to Win7 from XP, and it allowed for people to still run XP programs until they did migrate.)
That's not what it's for... It was meant to run programs that couldn't deal with the features in 7, but ran in XP (or previous versions). Think older software or in house developed software. The market wasn't you and me, it was an enterprise
Second, what's the easiest way to backup my XP Mode configuration (installation, I guess) so that if somethings goes wrong, I can simply restore it from a backup without having to re-install XP Mode?
I would think you just need to copy the virtual hard drive file
You would need to reinstall the bits for XP mode if you ever had a need to reinstall. The app was released. It's not going away until there's an end of life for win 7 and even then...