Q1. What is the problem that you are trying to solve?
When a user leaves a group, or is removed from the a shared list, or is deleted, all password he has used or seen should be marked for renewal. So he no longer can use the password he might saved somewhere else.
Q2 - Who is impacted?
Everybody who removes a user from a group.
Q3 - Why is it important and/or urgent?
A password which isn’t shared anymore with specific user, should not be used anymore.
Q4 - What is your proposed solution? (optional)
Tag all passwords for renewal which where loaded by the user from database. No need for changing passwords user never used or seen.