For some insight, the issue with the mitral valve is that there is backflow of blood back into the upper chamber when the lower chamber pumps and if significant there will be a reduction of cardiac output (CO). This can cause an enlargement of the upper and lower chambers (dilated cardiomyopathy, DCM).
MR (mitral valve regurgitation). The backflow of blood is severe and should have been treated before the ventricles enlarged. The enlargement will impose a burden and stress to the heart that many surgeons try to avoid and will operate only when the situation is critical. Good systole function indicates the heart has good contractility inspite of the enlarged heart...but left untreated the heart will lose its contractility (pumping power) and cause heart failure.
The problems with your father's mitral valve are due to the leaflets not closing properly to cover the valve opening when the heart pumps. Torn chordae will not have proper control of the leaflet. Chordae is stringlike or a chord, if you will, that attaches leaflets to the heart wall. Torn chordae will enable the leaflet to flail and not close properly.
An ECG would not provide the information you have cited. Your father probably had an echocardiogram. What can be done is for your father's doctor is to try with medication to reduce the heart's workload and possibly normalize the size of the left atrium (LA) and left ventricle (LV).
Mild AS refers to aorta valve (valve between the left ventricle and the output tract. Aorta stenosis (narrowing of the valve) is mild and almost always of no medical significance.
Hope this helps, and if you have any further questions, you are welcome to respond. Take care.