In the case when your colleague leaves the company, you can easily transfer the license to the new replacement.
To do this, please open Settings in the main menu > Team > click on 3 dots near the name of the user who left the company > Delete. Then click Invite new users on the right. Type the email address of a new user and choose a Team Role for them. Once done, this person will receive an invitation to the email address and need to accept it.
Please refer to our Help article for more details.