I doubt Apple will be removing OpenGL any time soon (at least in the next 5 years, probably more). Feels like it’s more of a marketing move for metal. But sure, it’s possible that Apple is arrogant enough to actually do it. However, I think they would have to give another notice plenty of time beforehand, as a big portion of old games/graphics software would stop working. (Also if not many people migrate to metal early it should make the decision to remove OpenGL harder for them.)
While the SDL2 drawing API is quite enough for old school 2d games, not having shaders is really a non-starter for me, even for 2d stuff. So for a modern looking 2d game the solution would be to make your drawing code independent enough from other code, so that it’s easy to implement multiple drawing backends.
My game is 3d, but simple enough to work nicely on ~all platforms using OpenGL. So I’m not going to be adding another drawing backend just for Apple. Personally I will just drop Apple if they drop OpenGL, but obviously that is not an option for many people.