Yeah, I never really cared that much about Classic, but seeing how Jagex has handled this incident makes me feel uneasy about it as well. I'd imagine that RS3 has around 5 years left to live if its core issues like the MTX isn't fixed and the decline continues, while for OSRS it's harder to say anything because it has kept steadily growing these past few years.
"Volat Accipiter libera est; venandi sua natura est."
~Accipiter striatus