Seems simple enough to clear any calibrations/recipes, and it'll take years to get that back without the right tools/know how. Maybe pull the filters on the clean room on the way out the door, too, really burn that bridge.
Unfortunately though, there's always one guy in the office who knows how to get the machine running, even if it's a pile of smoldering charcoal, with a not-approved-by-IT USB drive that has backups of the weirdest stuff, from three updates ago.