I had a similar situation, I was the local IT and he thought my position was redundant, he decided to play silly buggers. Got a new position, wrote meticulous documentation, made sure I left everything in order.
He didn't actually understand my role, but soon realised.
Whatever instructions/documentation etc would not be followed and calling me two days after I left and started my new role, that I wasn't going to "do him a favour" and bail him out of brown stuff.
It cost him a weeks wages to get me back in, in cash before I set foot in the area the fault had occurred.
Despite me telling me repeatedly that spares are good in time critical situations, it backfired spectacularly when they lost around 100,000 quids worth of production, a production line crew standing idle for what should have cost 1600 in parts and one electrician following instructions to restore a backup to a touchscreen. He had to wait till morning to get a refurbed screen,
I left site 10 minutes after I arrived, a huge grin and a perfect tale for future employers that documentation, courtesy and spare parts can really make a difference, and Schadenfreude is real and so, so satisfying.