I've been in that situation.
Was laid off from my position with several others for cost-cutting reasons (execs had made some bad business decisions and it bit them in the butt costing a half dozen jobs) Before being walked to the door, I asked the guy replacing me to change all admin passwords and terminate my VPN. He was part-time and found a better gig within a month of me leaving. After he left (went overseas) and before they found a replacement, several servers went down (log files filled up the HD on the DC, they needed constant attention) and I had cops knocking on my door questioning me. I was being accused by execs at my former company (same ones who laid us off) for trashing the servers.
Luckily, I had the email chain showing I no longer had access and proof all passwords had been changed after I had left. They went away and two days later got a desperate call from my former boss asking me if I wanted to come back and help them recover. Already had a new job offer several hours away and said no. I heard it took them two weeks to get server access after engaging a consultant. It was another week until they had everything back up. The new passwords had never been documented, my replacement never responded to email and I heard from friends at the company that I was still being blamed for the incident by the execs.