It's one of those things where it doesn't really matter at this point. It's essentially the "once a cheater, always a cheater" mantra.

Imagine a professional athlete getting caught doping. Like Lance Armstrong in cycling. Then imagine they just let him compete in the Tour de France the year after and he dominates again.

No amount of blood testing would ever make people believe Lance isn't cheating somehow. He proved he was a cheater and he proved he could get away with it under scrutiny.

Same thing here. It's been proven he's cheated and a lot more than he admitted to when questioned. Thus he's "a cheater".

He may legitimately be worthy of the rank he holds these days, but no opponent (or fan) will trust him ever again. Does chess as a whole want a world champion who might be a cheater? Nope.