Use case is:

• User updates the Jenkins master version
• VersionColumn takes the slaves offline due to incompatible slave version
• User forgets to check if slaves are running OK

Enhancement request to send an email to administrator (should be configurable...) when slave(s) are taken offline due to incompatible version.

One way this could be achieved is by integrating with Node Offline Notification Plugin. This plugin sends email notification if any slave goes offline due to network disconnect / crash / etc. However the deliberate taking offline by VersionColumn does NOT trigger this notification presently. (In that way the email address is only configured in one place for both plugins)