Is it safe to use a pizza stone that was left in the oven after the self cleaning process? It now looks like new, but I'm not sure it is safe you use.
I'd still use it but let me insert the disclaimer that ANY safety information you receive here is opinion and should be taken as such. It is very possible that the manufacturer would recommend you not use it any more.
There's no reason why it shouldn't be safe to use unless you used some sort of chemical oven cleaner on it. Commercial pizza ovens get up to 700 to 800 degrees.