What happens when you delete a user or client?

Deleted Clients

When you delete a client, all of their projects, estimates, profiles, invoices and expenses will still be available in your account. However, you will no longer be able to send them new estimates and invoices.  When generating reports, deleted clients do not show up in the list of clients that you can run reports on.

You can always un-delete a client at any time.
Deleted Users
When you delete a user, all of the job reports and time entries they had entered are still available for viewing and all of the projects, invoices, estimates, expenses, etc. they created remain in your account.