Hi Miss Do. Well you don't HAVE to cancel your plans for Sipadan. You are deciding that the risk is too great to visit there, without insurance, which is a personal choice. There are plenty of opinions that will tell you the risk is minimal and that it is bordering on the criminal to visit Sabah to dive and to not dive Sipadan.
Also if you are ruling the east coast out completely, there is not really anything else that could be called world-class. TARP in front of KK? Mantanani? Not really worth getting wet for. OK if you are in KK and decide you want to dive. But to travel all the way from London? I would urge you to reconsider Sipadan. Or extend your stay in Layang Layang, which is the only world-class is the only place outside of the east coast.