I just want to point out that one of the beautiful parts of TWD is that it does keep on going. Most zombie stories only focus on the start of the outbreak, but doesn't show how things evolve as time goes on. This is what made TWD different.

But I agree, eventually it needs an end, even if that is everyone dying/infected.

The Last of Us needs to end because it's based on an existing story that has an ending. Don't invent new stuff, just tell the story that needs to be told and then end it.