I think you can still retake as there is gonna to be a legacy paper available for the Year 12 (now Year 13) who started Sixth Form Sep 2014.
The way I see it:
1) Take a gap year/resit exams/reapply....this route allow you to retake your exams and you may like to work/take extra A-levels, which can help to stand your UCAS application from others. And having gone down this route myself, I am very glad I did it, as I got the grade I needed for a better university and also sometimes uni might give you a lower offer than a direct school leaver. (Make sure you can get your hand down to do the work required, despite the absence of school and teachers!)
2) Clearing--If you are desperate to go to university, than is there any course in Clearing that you like?
Marvel