I suspect a deeply hooked fish is likely to die no matter what you do. I guess the question is what course of action gives the fish the best chance to survive?

Here are some past discussions on this topic.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=20;t=000396#000000

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=20;t=001330#000006

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=20;t=001048#000003