Umbraco version 8 is almost End-Of-Life (dead). Or is it not? How does that work with STS and LTS and migration?

We already wrote a little article 1.5 years ago about the EOL (End-of-Life) of Umbraco 7. Now it is Umbraco 8's turn. More and more clients ask us how that works now? Do I have to migrate immediately when Umbraco tells me to?