I know some drift a bit on their implementations over time, but have not be wholesale yanked out.
Obviously the solution to this is to not rely on these preview functions for production code. The way to do that is to run production in an LTS version of Java. I don't think that's an extreme point of view, frankly.
The new stuff is interesting and cool, and in time, it ends up in the LTS version.
Having lived through Java 5, 6, and 8, these are halcyon times for Java. It's moving VERY fast, and has been for some time.
Are there preview capabilities in the LTS versions? Yes, there are. But they're not under the LTS tent. Don't use them. The demarcation between the development releases and the LTS releases are a smart program to get features out into the world, and set some real lines in the sand for advancement. It helps keep preview items from staying in preview mode for an indeterminate amount of time.
And the two year LTS release cycle for a notoriously conservative eco-system is ample.