In the International court of justice decision on the claim of Ukraine against Russia will apply to breaches of the two conventions, but will not affect the most important question of the armed aggression. Why not consider the ultimate question? In your opinion.
Good job. Youve opened can of worms.
To answer you question straight up, however. You could then take to court
any major power in existence. Ie. any armed attack started by any country without UN approval. Which would mean that court would be too occupied by accusations from all over the world against United States and Britain to deal effectively with real politik of Russia.
So, no Russia is not going to get even more roasted, because it would undermine the international court.