Believe it or not, Hard drives can take a lot of heat and still be recovered. Just so long as the temperature did not get above 1,221°F (Which is the melting point of Aluminum) there is a good chance it can be recovered. Notice that the iMac above got so hot that it melted the Aluminum case but the hard drive inside did not quite reach the melting point of aluminum.
Notice that most of the plastic inside the drive is melted.
There was also water inside the drive when the fire company put the fire out but this drive is recoverable because the disk surface is still shiny.
This Western Digital External drive was 100% recovered.
This drive got too hot and actually started to melt the aluminum.
(Notice the rainbow colors on the disk surface)
This drive was not recoverable.
Hard drive from the same fire in the same room were recoverable.
It all depends on how hot the drive got.