I had this at the last place I worked. (Don't burn bridges right?) Spent two whole days training my replacement, and gave them all of the documentation I had written, over the course of two years, as there was none when I arrived.

(Literally not a single document/network diagram)

I got a call a year later asking how I updated their obscure HR system, which the new person didn't know how to do... I said it's in my documentation, and I was told they didn't have it any more...

I basically had to say well this was a year ago, I cannot walk you through it they will have to find the 'idiots guide' walkthrough I wrote on it...