I know nobody at SuperUser like to hear It's Impossible™ but unfortunately, it looks like that is the case with Windows (at the moment anyway).
Windows, unlike Linux doesn't have the provision to update files as they're being used. On Linux systems, you can install an update for a program is currently in use and unlike Windows, Linux doesn't require process termination in order to finish the update.
Linux systems will let you continue using the older version of the program until you close it of your own volition. The next time you start the program, it will have updated to the new version. Linux achieves this kind of 'in-place file modifications' like this:
When you open a file, the kernel follows the link, and assigns the inode a file descriptor (a number that it keeps track of internally). When you delete the file, you are "unlinking" the inode; the file descriptor still points to it.
You can create a new file with the exact same name as the old file after deleting it, effectively "replacing" it, but it will point to a different inode. Any programs that still have the old file open can still access the old file via the file descriptor, but you have effectively upgraded the program in place.
As soon as the program terminates (or closes the file), and starts up (or tries to access it again), it accesses the new file, and there you have it, a completely in-place replacement of a file!
Source: toolbox.com
This opens Linux to the possibility of installing system upgrades without having to reboot the machine, and not surprisingly Linux and UNIX users brag about how they haven't restarted their systems since George Bush Sr. was president.
However, it may not be that simple (even for *nix users) and the UNIX/Linux systems that make do without rebooting for years aren't your regular desktop computers. Tools like Ksplice and live-patching support introduced in Linux kernel 4 definitely make it easier though.
It seems like Windows has tried to reduce unnecessary reboots over time and the newest versions can upgrade many types of drivers without the need for rebooting but it's just not as flexible as Linux in this type of situations.
As for upgrading an offline Windows installation, I couldn't find much on that.