You'd be like the guys coding Cobol. They thought they'd have a job forever. However technology moves on, new languages appear, Cobol was discarded, and they're out of a job.
Cobol isn't quite dead yet, There are 17 open cobol positions in my city right now, (all at banks and government agencies), devs who are well past retirement age are being paid insane salaries to stick around and employers are prepared to spend months training junior devs in the language.
Technology may move quickly but big corporations and governments do not, Zombie technology may not be all that flashy and interesting but once big business critical systems have been built on any platform it becomes very difficult to kill it completely and you can build a great career supporting that crap.