1. He plays basketball worse than football. 或:He isn't as/so good at playing basketball as (at playing) soccer. 或:He is better at (playing) soccer than (at playing) basketball. 或:He does worse in (playing) basketball than in (playing) soccer. 或:He does better in (playing soccer) than in (playing) basketball.
2. The older she is, the more beautiful she is, however.
3. 这要看你的句意是“即使地球现在灭亡”还是“即使地球将来灭亡”。 如果是前者,则只能用:Even if the earth were ruined, my love for you would still exist. 如果是后者,则两种都可以(另外一种是:Even if the earth were to be ruied)。