If a mounted filesystem disappears from the monitored system, the LLD discovery for Linux Filesystems marks the items and triggers as "not discovered anymore" and the user will never notice.

I suggest to add a trigger prototype to the Mounted filesystem discovery, named

Linux: FS {#FSNAME}: Filesystem is not mounted

with Expression

nodata(/Linux by Zabbix agent/vfs.fs.dependent{#FSNAME},data,5m)=1

and finally set the "Disable lost resources" option to "After 1h"

 

With this upgrade users will receive a trigger, when a mountpoint disappears.