Ah, get you. Sorry.
Well, maybe you would be best to put this loan in writing. Generally, a loan does not get written off because someone dies, it is repayable to their estate and so would form part of your father's assets (to be distributed according to his will).
However, if he wishes it to be written off on his death, it will then become an inheritance to you.
So, in either case, if it is not repaid, it will eat into your tax free threshold for CAT.