While is it not possible to delete a Staff member from Databridge you can make them unavailable and stop their access to the system.
The first thing to do is make the staff member not current. To do this go to the Staff member's Work tab and untick Current Staff. You may want to also remove the Staff member's email address.
Next remove them from any sites they may be associated with. Go to the Security tab and locate the Sites section. Click the notepad icon next to each site and untick Access to Site.
Lastly lock out their login if they have one. For this go to the Security tab for the Staff member. Tick the option Is Locked Out.