Once you continue to pay the A class of PRSI (which you will if you're working 32 hrs per week) your future entitlement to Illness Benefit will remain.
The option to reduce your hours and move to FIS sounds like a good one, if it's feasible for you financially.
If you claim Illness Benefit in the future, your FIS payment is only payable with Illness Benefit for 6 weeks, after that it stops until you return to work.
If you are on Illness Benefit for 6 months, and wish to return to work in a part-time capacity, you can apply for Partial Capacity Benefit (PCB) which pays a portion of the Illness Benefit rate in addition to your salary. This doesn't apply in your situation now, but may in the future. Note that you couldn't get PCB and FIS at the same time.