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