Hopefully you will get an answer next week. I would advise against telling the university to reject him at this stage, when A level results aren’t even out. If you don’t hear early next week, ask for a firm date by which they know they can decide.
It will probably depend on whether the HL subject(s) that he failed are relevant to his degree. They are more likely to be, by virtue of him choosing to study them at HL, not SL.
There is still a lot of information missing. What was his total score out of 45? How many HL did he do - 3 or 4? What was the mark in each HL individually? If he got a total of 11 in HL I am guessing he did 3, so got something like 5, 3, 3 or 5, 4, 2.
As you say his total point score is over the pass mark, and he got 11/21 in the HL, he must have got 14+ in the SL subjects. I’m going to guess he got 2 or 3 out of 3 in the core. So we’re looking at between 27/45 and 32/45. That’s quite a range, and we don’t know the subject he has applied to study, so we can’t tell you whether am applicant with that score would likely be able to get a degree place or whether he would do well to retake and defer entry.
Also, what did his university offer actually say? Did it require grades he hasn’t met in individual subjects, a total grade he has just missed or did it specify that he must achieve the diploma certificate?