This is not my field of expertise, but I am a relief LSA, I have only learnt about IEP's in college, but I am expected to give 1-1 support for children without knowing where they are, targets etc.
I mainly work with 1 child continuously and another child for 15 mins literacy and 15 mins Numeracy everyday.
The LSA I am covering is long term sick but for the past couple of days we have so busy trying to get the school nice for open evening etc, myself and the other LSA's just haven't had the time to work with the children.
Its a case of having to squeeze it in when we can.
This is only because the school have been getting ready for open evening etc, the same at christmas, with everything going on there wasnt time to do it everyday.
AFAIK IEP's are not legally binding, they are set for the child with targets to work towards.
It depends how long the child hasn't had the help for, if we are talking a few days then I don't think it can be helped but if we are talking a few weeks then that isn't acceptable IMO.
Sickness is something that happens. The school I relief for (I only do one school) has 3 relief LSA's that they use, me and another one pretty much come in at an hours notice. I have left my mornings open specifically in case the school phone (I work a regular job around this).
It also depends on the degree of the IEP and how much help the child needs. A school action needs only a tiny bit of help. Whereas a statemented child needs more help.
It's about priorities