First and foremost, great choice, you have eloquent taste in my opinion!
The rose gold plating is real gold actually, but I think what you meant is that it is a layer of plating as opposed to a solid case construction.
I have in my possession RG plated ROOs for 2-3 years now, and my experience is that the fading is minimal, if not non existent.
In fact, I have just ordered a rose gold 15400, and am anticipating its arrival.
If you like the watch, buy with confidence! The plating on the watch will last long enough.