If you can write well, take an interest in history and were a high achiever before you dropped the subject, you'll be fine! The AS course is often different to what you would've studdied at GCSE, anyway. You may find it hard, or you may not, but not taking it to GCSE will have little contribution to this.
Of course Arts subjects are better preperation for Law careers. But with English and Latin already, I don't think you'd even need History. Chemistry would go very well with your Biology. Taking Latin, is very impressive.