If you dismiss a user, he/she won't be able to log in to the Bitrix24 account and your company's data will be safe.
How to dismiss an employee?
Open the employee's profile page, click the Actions button and select Dismiss.
You can also dismiss an employee by clicking the actions button next to the name in the list of employees.
How to hire the dismissed employee back?
To hire back a dismissed employee, use the Dismissed persons filter in the Employees tab. Then select the employee, click the actions button and select Hire.
This user will be able to log in to the Bitrix24 account again.