They did have a time limit on when they could take something to disciplinary level when I worked there, but that was a very long time ago.
If he hasn't had (m)any other disciplinary hearings then I wouldn't be too worried if they do want to pursue the matter as it's likely to end in a verbal warning at worst. That said, the majority of the absences were due to illness that could have been spread to other staff members or, heaven forbid, customers; if it does go to a hearing, make sure he stresses that point as everything said is recorded and the company would obviously be unwilling to be seen to put others at risk.
The only problem I can see (as long as he followed correct absence procedure - ringing in however many hours they ask before the shift is due to start) is the absence due to taking you to hospital. They might be a bit iffy about that.