ProlificLurker sorry to hear that your DS 'bombed' his mocks but it's surely not too late for a turnaround in academic fortunes? Isn't it quite common for DC to underachieve at this stage?
I guess the main thing you have to look at is this a 'blip' or does it reflect his grades/pattern of results throughout the sixth form? I'm presuming it's the former given that he's clearly made aspirational university choices?
Does he have 'form' for this (i.e. did he perform similarly in GCSE mocks and then 'pull it out of the bag' for the real thing)?
I guess you need to think strategically about his firm and back-up offers. Maybe still get him to aim high (if he thinks he can turn his mock results around) but with Coventry as his fall-back?