Yeah, that's a good point, and definitely worth mentioning, but obviously rebooting isn't going to help in that case either. The parent was asking about how they would know if they need to reboot or not.
You're testing what happens when you delete a file for which an open file descriptor exists. On Linux, a shared library will normally be memory-mapped but will not have a corresponding file descriptor. So lsof will show DEL, not (deleted).
I wouldn't normally nitpick about something like this, but if people follow your advice they might incorrectly think they don't need to reboot.
sudo lsof | grep lib | grep DEL
You can then either reload those processes manually, or just bounce the box if that's easier.