its a difficult problem this. I wouldn't cut them off but I think perhaps try and make an effort to get back to being good friends with them, perhaps by speaking to a couple of people individually rather than as a group. At the same time, don't neglect other friendships. Sometimes, well often, in life friendships just end and there isn't really a dramatic reason for it. I wouldn't get too concerned and if attempts to rekindle the friendship fail, then just try and find new ones. Don't resent them, stay on good terms and now you've got two groups of friends. My advice would be to make an effort to repair the friendship and at the same time try and pursue new ones. Pick whichever makes you feel better or hold onto both. After you leave sixth form these friendships more than likely won't last so it's honestly not as big of a deal as it feels at the moment. This kind of thing just happens and its important to try and move on from it... its natural, try not to overthink it!
Let me know how it goes. All the best!