Question: are the induced arrhythmias permanent or do they discontinue when HCQ therapy discontinues?

I'm curious as to the permanency of the damage.

the qt prolongation of heart rhythm goes away once discontinued.

Qt prolongation does not mean you have arrhythmias. You don't get tachycardia or atrial flutter or necessarily sympthoms. Clinically if it means there is a risk if the QT interval gets to long that you will have a fatal arrhythmia - torsades de pointes. So you need to know how bad the Qt prolongation is. In the paper 2 patients had serious side effects - one with QT prolongation over 500ms and the second with a first-degree atrioventricular block. Another maybe had a left bundle branch (not great, but not fatal). They resolved by stopping HCQ treatment.

I didn't claim that the QT prolongation implied arrhythmia.

Wouldn’t ecg changes be plausibly the result of the virus itself? I haven’t read the paper so maybe they go into greater detail but it would be important to know whether such changes were seen in the control group as attrition/discontinuance is critically important to any study.

Well they're the most frequently occurring serious side effect of HCQ, so I'm not sure why you're leaping to blame the virus when the drug they're giving is well-known for causing exactly those problems.

Those ECG changes aren't generally observed just in people who have COVID-19; it's the drug that we know does that, doing that.

I imagine this question would be sorted out by looking at the control group.