Hello Jerry,
We’ve heard that SOME airports are no longer asking foreign residents to register their departure, but many still do.

In any event, if you forgot, when you get back show your residency card and explain the situation to the immigration official. They might ask for some proof of your departure date, so take your flight receipt with you.

The most important thing is not to re-enter Mexico as a tourist.

See this article for details about procedures
https://www.mexperience.com/entering-and-leaving-mexico/