What in the world are you supposed to do

when the enemy team's most fed carry is a tank with a billion HP with enough damage to kill all of your carries?

last game had a ridicuously fed garen because my ryze top apparently couldn't lane against him (I tried lane swapping with him, but garen was already fed enough), and in teamfight phase, there was just nothing I could do because if I fought garen, the rest of his team would kill me and if I killed his carries, he would just kill the rest of my team and survive. :|