At the moment, when a mentor quits (and doesn't opt-out [[ https://www.mediawiki.org/wiki/Growth/Mentor_dashboard#M2:_Settings_-_ability_to_edit_the_mentor's_message,_claim_a_mentee,_and_change_the_mentor_status | using the M2 module ]]) or is blocked (long term block), their mentees are not reassigned. They have to be claimed one by one, as they apear to be active.
To have a continuity in service, maybe activated mentees (as in mentees who made at least one edit) should be automatically reassigned. ([[ https://www.mediawiki.org/w/index.php?title=Topic:W158swd6boycfpre&topic_showPostId=w1oegae46km97fh5#flow-post-w1oegae46km97fh5 | Suggested here ]]). If automation is not possible, we should provide a way for communities to reassign mentees //en masse//.
We receive requests from various communities time to time, asking us to reassign some mentees ([[ https://phabricator.wikimedia.org/search/query/Yb6x_BDZVn0y/#R | here ]] or [[ https://www.mediawiki.org/wiki/Topic:Wp0qbwu562vrp1jj | there ]]).