Casuals dont get sick leave, maternity leave, long service leave or anything like that. All a casual has to do is say that u want time off and then they wont give u any shifts or reduced shifts for the period u asked. And then after the period u should b able to start right up again. Hope that helps.
I asked for time off at Christmas time which everyone knows is a big no no. But as I mentioned I would be when I got employed they pretty much had too - was for a wedding (asked for 2 weeks off). It's just a case of having nice bosses, supervisors and being a good employee which makes them more willing to help you out if you help them out.
if you want time off you will get it. The catch with coles when I worked there was if you hadn't done any shifts for a month then you were struck off the payroll, so its good to go back every fortnight to do that 4/5 hour shift.
Whether or not you'd be guaranteed a position when you return depends on the manager.
My manager is a complete ditz so as long as you ask her a week in advance to put you back on the roster she will.
For example, we just had an employee return from America because she went on exchange for 6 months.