Two reasons that would prevent a user from being deactivated are that the user is part of a territory hierarchy or that the user is assigned in workflow email alert. A territory hierarchy is a structure that defines how territories are related to each other in Salesforce; if a user is part of a territory hierarchy, they cannot be deactivated until they are removed from all territories. A workflow email alert is an action that sends an email to one or more recipients when a workflow rule is triggered; if a user is assigned in workflow email alert, they cannot be deactivated until they are removed from all email alerts. The user being in a custom hierarchy field or being the highest role in role hierarchy are not reasons that would prevent deactivation; they may affect data visibility or record ownership after deactivation, but they do not block deactivation itself. Reference: https://help.salesforce.com/s/articleView?id=sf.users_deactivate_considerations.htm&type=5

Two ways that marketing users can now access converted leads for editing are:
Find them in the global search result, by entering the lead name or other keywords in the global search box and selecting Leads from the drop-down menu. Converted leads will appear in the search result with a check mark icon next to them.
Utilize a list view where lead status equals Qualified, by creating or modifying a list view on the Leads tab and adding a filter for Lead Status equals Qualified. Converted leads will have Qualified as their lead status and will be visible in the list view. Searching the Recent Records component on the homepage or using Data Import Wizard will not allow users to access converted leads for editing. Reference: https://help.salesforce.com/s/articleView?id=sf.leads_view_converted.htm&type=5

To route new leads to the correct sales person based on the lead address, the administrator should use lead assignment rules that specify criteria based on lead fields such as City, State/Province, or Country, and assign leads that match those criteria to queues or users. Lead assignment rules can be triggered automatically when leads are created or manually by users. Creating a formula field, assigning with an escalation rule, or configuring a validation rule will not route leads to sales people. Reference: https://help.salesforce.com/s/articleView?id=sf.leads_assignment_rules.htm&type=5

When you delete a custom field, the data in that field is stored for 20 days before it is permanently deleted. During this time, you can restore the field and its data from the Recycle Bin or use Data Loader to export the data. Reference: https://help.salesforce.com/s/articleView?id=sf.customize_del_field.htm&type=5

Making a field universally required is a way to ensure that the field needs to be filled on every record; it prevents users from saving a record without entering a value in that field. It can be used to ensure that the billing system field needs to be filled on every invoice record by making it universally required in the field settings. Creating a process builder to set the field, defining an approval process for the child, or requiring the field on the record type are not ways to ensure that the field needs to be filled on every record; they either do not enforce data entry or only apply to certain scenarios or users. Reference: https://help.salesforce.com/s/articleView?id=sf.customize_fields.htm&type=5