What elements of sql server are impacted due to removal of domain/AD?

Sql server contains logins from 3 different domains (Under security\logins). These are mapped to database users. There are 15 databases. One of the domain/AD is planned to be decommissioned next year. 1. What elements other than login and users need to be reviewed to ensure there is no impact to sql server functionality, any jobs, sql server service account, etc? 2. Assuming domain3 will be decommissioned, what is the process to modify the login and user to domain1? For example- on the sql server, is a delete and create required or is there any way to modify existing login/users?