Lip or fin hooking the fish and dropping it back into the depths before snatching the hook may decompress the fish, but will not prevent damage to the fish through gas bubbles forming in the blood. If the stomach is protruding from the mouth the gas bladder has already burst and the air has entered into the gut cavity through the rip. The chances of that fish surviving is nil, according to Jeff Render of Louisiana State University. This is the case even if the fish has had its gut cavity punctured to release the gas. One experiment with red snapper revealed all fish hauled from 40 metres had internally ruptured air bladders with 5-7cm rips in their air bladders.
Shallower depths can also kill as well.
Fish hauled out of water depths as low as nine metres take more than 10 hours to regain their equilibrium in the air bladder. With the laws being what they are, we are currently instructed to return undersized, but not necessarily small fish, with little or no chance of survival. We legally condemn to death quite a large number of juvenile fish this way for no good reason other than to make a reasonable meal. However if those fish were kept they'd form a useful part of the species bag limit. The fairy tale that the act of returning small fish will allow them to grow to a breeding size is now proven to be a myth.