Adding someone to the Offboard group assigns them its offboarding checklist, so work through it before you remove their access. It’s an Administrative checklist, so an Admin completes it for them and the leaver never sees it on their portal.
Their record stays, but the People tab hides people who’ve left until you tick Removed in the Account Status filter.
What we recommendReassign what they own before you offboard them, as roles and document assignments don’t move by themselves. Roles & Groups on their sheet shows what to hand over.