Surely drive belts should be protected from debris by suitable cowlings? Even if this notorious belt was taken out by a stone, it is indicative of a design flaw. Or of course it could just be bad lack. Belts do go.
Either way I find it hard to believe anyone could prove beyond all doubt that a stone derailed it. Even if there were evidence on the pulley, it would be far more likely that some highly trained Renault spanner monkey left his 10mm socket in there.
Regardless, Renault will not be held accountable. They have a history of not giving a s**t. From the day they decided to mug-off the poor 400 customers who thought they had bought an exclusive limited edition Clio, to the day they decided to continue fitting chairs upholstered in tissue paper. The only answer is to vote with your wallet and buy cars made by manufacturers who possess at least an ounce of integrity. Crying shame, as they are capable of building some truly awesome drivers' cars. If only they gave the first f**k about the people who buy them.