...stop playing Warhammer (40k) altogether?
Maybe your favorite army gets smashed into the ground.
Maybe the prices have gone too high.
Maybe they removed your favorite army from the game altogether.

It doesn't matter how unlikely it is to actually happen, but what would cause you to say "and now i am going to STOP playing this game"?

For me personally it would most likely be if the prices would go up, especially for the core units.