Helicopter behavior

[speed150mph]

I'd say it's fairly realistic that they'd keep attacking for several reasons.

1: they are probably pretty pissed off at you for sinking their ship and our for vengance.

2: the helo has limited fuel range, and if they have been chasing you down for a while then that is probably pretty depleted so it's likely that unless they were less then 150 miles offshore that they probably wouldn't make it to land let alone an airbase.

3: it's not really suicide. Unless the ship suffered a catastrophic hit to a magazine and sank in a couple minutes it's safe to say that a good portion of the crew got out and are floating around in a lifeboat. The helo would have radioed a distress call if the ship didn't and would know that rescue was coming. All they would have to do is ditch near the lifeboat while they still had power, get picked up, and song sea shanties while they waited for someone to show up.