Where do warriors go when they die?

Depends on what they fought for and who they fought for.

Some Warriors go to Star Clan, but evil ones that did not follow the Warrior code go to The Dark Forest.

It is the place of no stars, or the dark forest, where the evil go.

The good warriors go to Starclan, where they hunt in prey-rich forests and live among the stars. If you go to StarClan, you are part of or you watch important ceremonies like when a cat is apprenticed to the medicine cat or a leader gets their 9 lives.

So they go to either StarClan or The Dark Forest.