Appropriateness of medical care

[chapo]

Dear Dr, I am after some guidance in understanding the medical approach used in the case of my father.
In 1999, he had a TIA, was taken to a country hospital and had ECG - no acute changes
Cranial nerve and limb power functional tests. - Normal.
He was on Warfarin after previous CVA, AMI and DVT six years
before.  The Hospital DR said as he is on Warfarin there is nothing more you can do. He was sent home and saw his General Paractioner. I don't know what she said but no investigations were carried out.
18 months later he had a disabling left sided CVA and subesquent tests revealed an occluded left I.C.A. He was seen by a neurologist he said that occlusion caused the stroke, but it was too late to open it back up again.
Since this time I have read many web sites and books and all say that TIA investigations should include MRI/CT and at least a Carotid Duplex as that is the most common source of emboli.
I know it is a difficult thing to ask but as he had no tests and considering the outcome is it fare to say his care was grossly lacking.  Further I would now like to question the Dr's in a non confrontational way.  What are the questions I should ask them.  Thanks in advance.