Idk, I’m out of the loop when it comes to whatever’s been going down with Facebook (should I even be worried?) and have been using my saved data from Facebook to play this game for a bit over two years now. I assume also linking it to my Apple ID is extra insurance.
It won’t matter as long as you save your game key somewhere safe to get any linking fixed.
You should. If you accidentally delete the game you will lose ALL progress you made. But, if you link with Apple ID/ Facebook you won’t have to worry about it.