She has only recently left hospital after two months and had to be looked after by family and friends while Van Diest returned in New Zealand.
Some of his friends told Van Diest not to return, but he thought that wouldn't be right, family friend Ingrid Otene told APNZ.
Van Diest's English isn't too good but Mrs Otene, speaking on his behalf, said he was "really please he did the right thing".
"A lot of people were saying, 'you don't have to go back, they'll never find you'. But he said for how own peace of mind and own integrity, he would not be able to face himself in the mirror [if he didn't return]."
Van Diest arrived in the country last Wednesday and on Friday went to the Manukau District Court, where he was convicted on each charge, disqualified from driving for six months and ordered to pay each of the three occupants in the car $500 reparation.
He's now on his way home.
Originally Van Diest and his wife had planned to travel to Invercargill by car the New Zealand leg of a trip that also included Singapore and Sydney.
Van Diest's lawyer Kahu Barron-Afeaki, SC, said although the sentence might appear light, it took into account all the circumstances, including that Van Diest's wife was the most seriously injured.
"He'll have to live with that for the rest of his life. For me this is a story of an honorable man rising up after a tragedy, doing the right thing."