I've read through a lot of the monash rules and legislation (they have their own law named after the university,
i'm not even joking).
If you commit some kind of serious non-academic offense (stalking, punching out your lecturer, etc) its pretty certain you'll get thrown out and even banned from the grounds. They can make you stay away for a certain period and that expires or they can ask you see a counsellor as part of your conditions but otherwise, it doesn't look too good for you. This one is pretty hard to do though, just dont be a dick.
If you fail more 50% or more of your units in a semester, they'll send you an email encouraging you to talk to the faculty and telling you about the kinds of services they offer (counseling if you're having pscyhological issues or problems adjusting, learning skills/ english help if your problem lies there, etc). If you fail
over 50% of your units (>50%) in any two consecutive semesters, it's fairly certain you will get into some measure of shit. An academic progress committee will examine your case. You may have to write a letter or something. They can hold a hearing you have to attend where they ask you questions and decide what to do.
Even then, unless your learning conduct has been especially heinous without good reason, they won't throw you out (as far as my understanding is, i dont guarantee this at all nor is it advice).
They may make your enrollment conditional on you lifting your marks or checking in with someone once a week or going to counseling or something like that. They really do want you to stay in the university, they do have hearts. If you have had legitimate issues, they want to help you. Likewise though, unless you have some kind of serious condition that continually affects your performance (some kind of disability, long term psychological conditions, etc), if you don't improve or take effort to improve, they might suspend you for awhile or totally boot you out. Again, it's not something they want to do, it's rare and if you've gotten to that point despite all the help, its your fault really.
Thanks. let's assume I had failed one or two units and couldn't meet the prerequisites for the coming units, if I repeat the units I had failed..and lost a semester or something...in that case do I graduate in 5 years and a semester? or 6 or 7 years?
As noted by others, there is a maximum duration.
I'm not sure about all faculties (they have different policies sometimes) but in science, i'm fairly certain you can only repeat a unit twice (up to 3 times total i guess) by default. Anything over this and theres appeals and forms and all kinds of things.
Unless you have some condition or problem which hinders your performance in general (which you should notify the university of, you can get special arrangements and consideration), there's no good reason for failing a unit 2 or 3 times over if you're putting in the work. Its easy to drop the ball in uni and we all do to a certain degree but if you're in a situation like this, you've dropped the ball so hard its on the other side of the planet.
Many people have fails. Ideally it shouldn't happen and it really screws up your average mark (which employers look at, its also considered for post-grad admission) but it does happen fairly often. Many people go part time/swap courses/are in doubles or other combos/etc which results in people finishing their degrees at different times. Everything is pretty free and easy at uni, i wouldn't rush.
That said, if you are failing, it does suggest a problem of one variety or another. If you failed in one semester, chances are you'll fail in the next one unless you fix the problem.