This happened to me. Was the sole developer on a certain service. Other engineers would use the service at the company, but no one else really wanted to get into it and work on it.

Was working on fixing an issue one morning, got roped into a meeting, and escorted from the building. Next week, saw an email from a coworker asking how to do something with the service. Told him, politely (don't burn bridges) that I didn't work there anymore and wasn't interested in helping that company without payment. Yeah, it might be thought of that I hung him out to dry, but that wasn't my intent. I just won't work for free, particularly when I was booted without much chance to get my affairs sorted