I spent 3 years working on scala tooling in my free time. One of my libraries is used by the vast majority of scala users (it is a dependency of other widely used tools). There was growth from 2018-2023 but it has flatlined over the last year. Right when theoretically it should be getting the boost from scala 3 having now been stable for a bit.
Personally I feel that scala has too much in the language and the compiler is too slow. The tooling is pretty good but it is finicky and ends up getting slow and/or unreliable with larger projects. Even if I were to restrict myself to a small subset of scala, I would still be unsatisfied with the long compile times which was the primary reason I decided to move on.
I don't know if I agree with your contention that languages can't die like COBOL. I think you can relatively easily keep a legacy scala system up, put it in maintenance mode and write new features/products in something else. That is what I expect is already happening with scala and that this trend is likely to accelerate. Keep in mind also that Martin Odersky is nearing retirement age and it's really hard to imagine scala without him. He has much more power/control than the head of most languages.
IMO, there's rarely such a thing as maintenance mode. Projects constantly evolve, and in turn this drives more investment in tooling and the ecosystem needed to keep those projects up. And this investment is what eventually drives more new projects and fresh blood, keeping the language fresh and in demand.
Again, look at Java.
Ofc, there's always the question of what happens with a market that isn't constantly growing due to zero-interest rates phenomenon. I guess we'll see, but IMO, that's problematic for newer languages, not established ones.
I too am a contributor of very popular libraries and am very familiar with ecosystem. One thing to keep in mind is that the language's culture has evolved. When I picked up Scala, back in 2010, the Future pattern and Future-driven libraries were all the rage. Whereas nowadays people prefer alternatives which now includes blocking I/O (Loom), with Future-driven libs being a risk going forward.