What voltage is CPU at? Check fans, check thermal paste application. If fans are not running, check connections. 99c is extraordinarily hot and will be thermal throttling well before even reaching that, as well as result in a reduced lifespan.
If taking it apart will void warranty then contact ASUS about the temps.
i have the same laptop and through ROG forum i found a BIOS version 307 which is unofficial but solved the frame drops issues
i have tested it myself and there is no frame drops. my temps are not high as yours but with the latest bios my temps are a bit higher (80-85c compared to 75-80c)