What would happen to a human body if a big brick was tied to it and it sank all the way to the deepest point of the ocean?

It would in the end implode.

Adrift level over the water the environment applies a weight of 14.5 psi (pounds per square inch) on our bodies. We have changed in accordance with this weight and can undoubtedly endure it. For each 10 meters an item plunges into the sea, an additional 14.5 psi of weight is applied on the body.

All things considered, when the normal individual sunk to about 20m the person in question would have suffocated by at that point. On the off chance that not, at that point they are in for an exceptionally agonizing knowledge.