After cremating a lady with her earring, the earring diappeared. Neden?

Very simple. Earrings must had melted in cremation and mixed with bones and ashes as a small bit of gold metal.
Gold melts at 1064 degree centigrade and cremation flame can give rise to this temperature, surely gold will melt after softening. The softening temperature is less than melting temperature.
HAYIR.
At least not in the sense that they will forever stay at 8mm. Maybe yes in the sense that even after a long while you might still see some trace of the previously present piercing. Maybe a dot, or a fold, or s small hole.
If you take out the ring or plug in a stretched earlobe, lets say 8mm, then the hole will shrink but not necessarily in a nice concentric way. So you could try and find or create a 7 mm (flared) plug or tunnel. In a material that is as light as possible. And then 6mm, and so on. Very slowly downsizing but while still wearing tunnels. In this way the hole generally closes ‘nicer’, but it is a lengthy process.
At 8mm there still is a good chance of a decent closure if you wait long enough. But the larger the hole the longer it takes, and there is definitely a ‘point of no return’. Some people have better vascularisation and cell turnover and heal easier and better. So it is difficult to indicate where this point is located.