This airplane is a twin and so would have had vacuum pumps on both engines. It is unlikely that both would fail at the same time. The NTSB said they were working.
Part of IFR training is to fly "partial panel". I had to do that as part of my training. What that means is flying with the vacuum instruments not working.
I had to make an IFR approach to minimums on partial panel.
It is difficult but if you have practiced it, it can be done.
One of the requirements to remain current for IFR is making 6 approaches in the last 6 months. A pilot should make practice approaches using partial panel as part of his normal routine.
This appears that he did get disoriented. That is easy to do if you haven't practiced. The jury felt sorry for them and gave them some money.
It was most likely just like John Kennedy Jr. He was flying a plane that was more than he could safely handle under the circumstances.