That bulbous area above the skull is called the melon and is represented in all modern cetaceans (whales and dolphins). Due to that, it should be fairly easy to reconstruct a sperm whale in the far future as long as there is still known record of the species.

Let's say at some future time when sperm whales have gone extinct and some future paleontologists have discovered sperm whale skeletons. How likely is that they'd be able to reproduce an accurate representation of these whales? Specifically, the head of the sperm whale doesn't seem to be represented by its skeleton. If you check this photo down below, you'll see that there is a huge gap between the top of its skull and the actual top of its head. I think this is the bulbous area where it stores its "sperm" oil. If these future palaeontologists had to reconstruct the whale, how likely is that they'll know about the bulbous area on top?

http://media-cache-ak0.pinimg.com/736x/49/a4/13/49a413b5cad4c45a6c7b6053aee96d18.jpg