It sounds to me as if your status currently with respect to this business is as an employee only, and nothing else ie unless you have a written contract of some type, I don't think that you would have a claim on the business. (I'm presuming when you say 'partner' that you are not married)
I think he needs to make a will pronto.
Otherwise everything would go to his next of kin, in the event of his demise, as per Irish inheritance laws in the absense of a will.
"In the event of not making a Will, a person’s assets and property will be divided according to The Succession Act 1965. In effect this means that your spouse is entitled to your entire estate if there are no children, otherwise two-thirds to your spouse and one-third to your children. If you do not have a spouse, your estate goes to your children. If you are unmarried with no children it goes to your parents and if both parents are deceased to your brothers and sisters."
This is very important to get sorted out. You should perhaps look at professional advise on this, especially given that the two of you are in the business together, but you may not have have any legal /financial protection at all.