On my "integrated" course, 1 guy (out of 20) didn't make it through groundschool and he called it a day about half way through the groundschool course. He was the living, breathing example of our flight schools wonderful "Safety Net" that reimbursed the student the bulk of their money spent so far (which worked out about £5,000 I seem to recall).
The one's that stumbled through groundschool all eventually got their CPL, except for one who seemed to have made up their mind they wouldn't be continuing with the course. That's 2 guys gone.
In the IR phase most people passed their IR first time or at least first series. There were a couple I think that dropped off the radar for a while and months later I heard they'd finished the course. This would have been easily 3/5 months later than scheduled so I've no idea what additional costs they might have incurred.
I believe there was another classmate who finished the course a year later than everyone else after running out of money then coming back to finish off.
So I suppose, out of 20, 17 got through it.