Don't know how you got that idea, but whatever. Titans are big enough to have entire ecosystems on them, and their ether forms dirt and stuff on stable areas. You'd have to have either a battleship or a real powerful Blade to do enough to one to actually hurt it.

As for the dying part, they live a long time, but not forever. The Titans currently around have started reaching the ends of their lifespans, but new ones haven't been being born.