The final sword battle with Sammo Hung's pirate leader was filmed on a sliver of beach at the very south of the island and it is the location I've marked on this post's location marker label (found at the bottom of the post). It's also a location that was used earlier as the Wu's made their way, under escort, to the pirate HQ. Those are the images you can see immediately below.
Seen from the direction of the water, this is also the same location used for the aforementioned final sword battle between Pai Ying and Sammo Hung. Who knows how long it took to film this particular battle, but you can see by comparing the two images below that it goes from very sunny to overcast, so it's possible it took a few days.
Finally, the last sequence we see in the film is of the fallen heroes' graves on a hillside overlooking the sea. It's a panning shot filmed moving to the right and was shot on the hillside above the previous beach battle location. The first image gives a nice view back towards Basalt Island (left) and Bluff Island (on the right). The final shot is looking westerly with Ung Kong on the left and Jin Island on the right in the distance.
This hilltop area is now occupied by a drug rehabilitation centre and so, I suspect, access for film buffs would be highly restricted, if not impossible. However, the serious film fan would probably be able to hire a boat past this part of the island. Trips like this can easily be arranged from Sai Kung waterfront for the right price (it's a fair distance so probably won't be cheap).