It is the uni's discretion whether they will accept you if you have an offer of AAB and miss that offer e.g achieving ABB/AAC.
If you are offered AAB and you get BBC, chances are they are unlikely to confirm your place. But it depends on the university.
If you are in that position, you could ask whether you could defer for the following year and take a gap year to do the exams again in summer. Or you make have to reapply to Universities again via UCAS.