I was sysadmin for a small ISP about 15 years ago. I was on vacation about 1500 miles away when I called to check in, the owner gets on the phone and says, "I deleted the entire /bin directory on [the primary web server], is that bad?" I told him to not touch it til I got home, and whatever he did do NOT shut it off!
Thankfully we had two machines which were virtually identical OS-wise (RedHat 6 if memory serves). I was able to get everything put back from the twin machine and keep everybody happy.
Thankfully that server kept running with relatively little issue the entire time even with all those core OS files gone. I don't think any customers were at all aware.
Open processes will hold open their files. So long as it's an 'rm' that you've run (which merely removes directory entries) and not a destructive action on the disk contents themselves, it's often possible for things to continue in a startlingly unaffected manner. Though not always.
The extent to which new calls to deleted files are made will have a strong impact on this.
Thankfully we had two machines which were virtually identical OS-wise (RedHat 6 if memory serves). I was able to get everything put back from the twin machine and keep everybody happy.
Thankfully that server kept running with relatively little issue the entire time even with all those core OS files gone. I don't think any customers were at all aware.