I have read somewhere only 1-2 a year out of 30ish guaranteed students failed before. The criteria for passing is like having 50+ average marks for the 8 MMI stations PLUS not having more than 3 stations <50. For example 4 45s + 4 75s would be a fail despite 60 average. Good thing is you only need to pass not have to compete against other students.
I guess if you fail you'll have to re-apply next year as a non-guaranteed student.
I'm assuming this is the chancellor's scholarship (99.90) pathway?
What do you know about the other 99 atar pathway? Is it also the same pass rates?