...
As of , the only relevant plugin is Manage Inactive Users. This free plugin also supports deactivating users in external user bases like Okta and Google Apps.
I am waiting on feedback from the author before passing judgement. The MIU plugin author released new versions that IMO bring the plugin into the realms of usability (previously even the definition of 'inactive' was completely opaque and unmodifiable). For users not keen on Groovy, I suggest giving this plugin a serious try.
REST Script
Without any plugins, the cleanest solution would be a script utilitizing Jira's REST interface. The script would search for inactive users with Crowd CQL, then deactivate them. A REST solution would have the advantage of also working on Cloud Jira.
...