Hi - you can use the Global Scheduler and Swap tool. The only downside is that you have to 1) select the projects (so you need to know which projects the person was on), and 2) you have to be in the Resource Manager field of the projects.
Now, luckily you can do a project report to see what projects they are on and then bulk edit those so you are the Resource Manager. Then you can use the global scheduler and action tool.
For your project report, you can use this EXIST filter, just swap out $$USER.ID for the ID of the employee you want to remove.
EXISTS:1:$$OBJCODE=ASSGN
EXISTS:1:assignedToID=$$USER.ID
EXISTS:1:assignedToID_Mod=in
EXISTS:1:projectID=FIELD:ID
EXISTS:1:task:status=CPL
EXISTS:1:task:status_Mod=notin