I know of people who received offers from Oxbridge with drama. If you enjoy it, carry it on. I would say both drama and classics have a degree of relevance to english. Email admissions tutors if you are worried because, ultimately, it's down to them. Also, I don't know how realistic this is, but there are a couple of other options:
-Carry on with all four to A2 but don't attend the classics lessons. If you're good at it, and only need C grades this year, is it possible for you to get the grades simply with some study in your free time? (as opposed to attending all the lessons, doing the homework and so on).
-As you are having a gap year, you could perhaps take the 3 A2 modules in that gap year so universities will see you (hopefully) three As and then that you are also taking classics to A2. If they hated drama that much, they could make your offer conditional on one A grade (classics).
But I'm no expert, I'd say email them.