[Jimbuna]

The reason your crew have stopped firing is because the ship is to all intents and purposes 'destroyed'. The actual act of seeing her sink afterwards is simply down to the time it is taking for it to flood.

The reason you received no renown could be for a variety of reasons:

Damage from contact with a mine.
Weather conditions were responsible for the final points hit
Attack from aircraft
Or simply one of those irkesome occasions that occur from time to time that nobody can find a definitive answer to other than...stoooopid SH3 game engine.