Putting aside speculation and the "you can't prove that they're not going to do it" argument, there is not the slightest evidence that Adobe is going to move Lightroom to a subscription model. Also, there is evidence that a substantial majority of actual paying Photoshop customers had already moved to the CC subscription model before the recent news about CS fading away. So, no matter how much some photographers might be upset by the CC move, I doubt that the PhotoShop/Lightroom training business is in trouble.
Also if other rival products do take significant market share away from PS, the PS/LR trainers will surely develop new training products for them, and they could even do better than now, because changing to new software likely increases the need for (re-)training help.