That's false actually. There is a "new" syntax, but the popularity of the language is in many ways due to the terse, easy-to-read original syntax—it's not going away and it's not deprecated.
You're right. It will be supported indefinitely through the gem - so neither officially deprecated or going away.
However, since .sass is no longer the primary syntax (nor default for Rails), and it's not supported by any new development efforts, it's safe to say that it is not the favored child.
However, since .sass is no longer the primary syntax (nor default for Rails), and it's not supported by any new development efforts, it's safe to say that it is not the favored child.