A user under a Microsoft 365 Business Standard (formerly O365 Business Premium) license reported to me today that all Office 365 apps have disappeared from her Win 10 Pro computer. No errors, nothing, the software is simply gone. Googling on this, most people focus on missing icons. This is not that. The software is gone completely, nothing in Apps, except the generic Office Click to Run icon that's usually found on Win 10 machines whether Office was actually installed or not. Malware is not suspected on this one.
The only slight clue I have on this is that, given that it's gone, I decided to first just re-download the installer after logging into office.com. Running the installer, it tells me an installation is already in progress, yet there are no taskbar/notification area icons. Task Manager shows some OfficeC2R stuff, which I tried to End Task. It wouldn't end, it would just pop back up again in Task Manager (but again nothing in the actual UI).
I did the Open File Location, found the exe for this thing, renamed it with .old, (surprisingly it let me without hassle), and upon doing that, I then was able to kill the now-memory-only OfficeC2R exe file from Task Manager. This then let me start the installer I had downloaded, which is currently in progress for downloading (though, extremely slowly, despite a 19ms / 120Mbps connection - MS having issues I wonder? - 11:35 AM Eastern May 15 2020).
So I suspect in some kind of dumb way, Office was updating itself and screwed up? The last Windows update was May 12, the quality update for .net framework. I'm not actually sure where to look in the event logs for stuff related to install/uninstall for Office - the started Application log shows msiinstaller stuff related to my installing it, but keyword searching for "office" shows nothing that points to a removal or an update of the software.