I just wanted to follow up this thread and say that we ended up staying on Mabul and felt very safe. We stayed at Scuba Junkie which exceeded our expectations in all areas. Lovely rooms, good food, good people and well organised diving with well controlled numbers.
Night diving is still banned on the island, but there was enough to see during the day to keep us very satisfied.
We only managed one day of diving on Sipidan and it was fantastic for wide-angle creature encounters (reef sharks, bumpheads, turtles, jacks etc) A big surprise was Si Amil which had world class muck diving. A dive on Meditation \Wall had me scrambling between subjects from Twin-spotted Lionfish and frogfish to a 20bar enounter with Flambouyant Cuttlefish. Then First Beach turned up a 20-bar Hairy Frogfish to make my last subject of the trip.
Mabul and Kapalai also had great muck critter diving.
I'm really glad we made the decision to stay on Mabul and visit Sipidan...it's very high on my return visit list. Mixed with the primate and other jungle life, Borneo makes a fantastic destination. Its just a pity the Palm Oil industry is so big...you have to see it to believe how vast the plantations are! very sad.
Thanks for everyone's feedback.