Your question is a little vague bit I suggest you get an outline of what is being proposed for you in writing from your hr or line manager, there should be no difference to the package available to any other employee unless there is any reduction in service accrual as a result of a lengthy absence.
I'm referring to one who is in receipt of sickness benefit and an opportunity has arisen for voluntary redundancy. Will sickness benefit be impacted on, if the person receives a redundancy payment. Given.. the person is certified sick.
Still vague, I think you are asking will they still get sickness benefit (from the State..? ) If they get redundancy, if that is what you are asking then I am not sure.
Sickness benefit paid by the employer if that is the case will clearly stop once the employment is terminated.