hi there, just to clarify, the number of international students coming (or not) does not imply that universities will take in more home students. Financially it does not make sense and legally, the number of CAS issued to international candidates is capped (with universities fined if they go over the number with huge consequences). They could of course, take more home students - but that's not based on whether internationals come or not.
In terms of whether published clearing grades of BBB will allow a C grade to get in - this happened to friends of ours. Child received ABC and the offer was BBB. Theoretically, the UCAS points add up, but they were still rejected. Turns out that the C was the issue for that institution/subject and their profile was considered in the run up to the release (remember universities have the grades about a week before the release), and ultimately rejected. This sounds like our friend was close and perhaps compared to the others in the pile, was just slightly lower than the others.
Regardless, they are very happy where they are now, and thriving, top 10% in the class, and glad of their final choice