In scenario 1,
no, the planes can’t hit the submarine if you choose not to submerge, because there is no attacking destroyer present.
There is not automatic destroying of anything in this scenario. It goes round by round. Each round, the submarine may submerge before the attacker rolls dice, but you have no reason to submerge because nothing can hit it.
The carrier can take hits from the battleship, to keep his aircraft from being hit until the carrier is gone. If he knows what he’s doing, he’ll retreat once the battleship is sunk because he can accomplish nothing more. Retreating is step #6 in the battle sequence, which comes right after step #5, remove defender’s casualties. So your sub’s presence there actually gives him the option to retreat UNLESS you submerge it before the battleship is sunk! (Because then there is nothign to retreat from) Note also that your sub’s presence gives you the ability to prevent his carrier from staying there, in that sea zone, after the battle because your sub is invincible and once your 2 boats were engaged, he cannot ignore the sub.
OK, there was a lot to that, so if you have any follow up questions, do not hesitate