Eh. What about updated libc.so or libssl.so? If daemons using them do not get restarted, they keep using the old version. If they do get restarted, well, then, it's just as if you rebooted the machine. Somewhat quicker, but in effect it's a reboot.

And you will never know if the updated libs cause segfaults (at best) or shenanigans (at worst).

You can replace the open files on Windows (most oth time, see my other comment here), but the decision to reboot is not a technical one (and back in the days many invested in no reboot upgrades) but to have less headache on a corner cases.