Ya, his data is probably screwed, but who knows. It's possible (longshot but possible) that the plastic substrate bent, but that's just a coating, so who knows the lands and pits on the disc still could be there. He already said he was able to read some of the data, at 80% he was obviously reading some data which had been "melted". If he can somehow manage to get the disc perfectly straight, he could have a slim chance of reading the disc, unless he turns up the oven too high
I'd put the disc between two perfect flat objects, the top one maybe weighted a bit, turn on the oven for a min, and if he's reeeeal lucky it may just work.